… yaml for doc (#7548)

## Context

Part of **Configuration Inversion (Step 1)** - Stack progress:
1. **→ [#7548](#7548) -
Add GitLab step and JSON configuration file (this PR)**
2. [#7688](#7688) -
Reorganize keys, split config keys and platform keys
3. [#7698](#7698) -
Generate ConfigurationKeys with source generator
4. [#7689](#7689) -
Aliases handling and analyzers
5. [#7697](#7697) -
Replace manual ConfigurationKeys by generated ones in the whole solution



## Summary

Adds centralized configuration registry (`supported-configurations.json`
+
[supported-configurations-docs.yaml](cci:7://file:///Users/anna.yafi/go/src/github.com/DataDog/dd-trace-dotnet3/tracer/src/Datadog.Trace/Configuration/supported-configurations-docs.yaml:0:0-0:0))
containing ~280 configuration keys with automated GitLab CI validation.

## Changes

**Configuration Files:**
- `supported-configurations.json` - Machine-readable registry of all
configuration keys with versions, aliases, and deprecations
-
[supported-configurations-docs.yaml](cci:7://file:///Users/anna.yafi/go/src/github.com/DataDog/dd-trace-dotnet3/tracer/src/Datadog.Trace/Configuration/supported-configurations-docs.yaml:0:0-0:0)
- Human-readable documentation for each configuration key

**CI/CD:**
- Added `validate_supported_configurations_local_file` step to
`.gitlab-ci.yml`
- Updated `.gitlab/one-pipeline.locked.yaml` to reference validation
template

**File Structure:**
```json
{
  "supportedConfigurations": { "DD_TRACE_ENABLED": { "version": ["A"] }, ... },
  "aliases": { "DD_AGENT_HOST": ["DD_TRACE_AGENT_HOSTNAME", ...], ... },
  "deprecations": { "DD_TRACE_ANALYTICS_ENABLED": "Deprecated - ...", ... }
}
```

## Motivation

Provides single source of truth for configuration keys to enable:
- Automated documentation validation
- Cross-tracer compatibility checks
- Configuration migration tooling
- Automated doc generation

See: [Configuration Registry Design
Doc](https://docs.google.com/document/d/1VIvOyQPfuQIWBIgNY68A9hzLir0-3eJijTwmpWASO8s/edit?tab=t.0#heading=h.jy2ajbk2b8ba)

## Validation

GitLab CI validates JSON structure, naming conventions, and schema
compliance on every build.

## Commit Details

**`2639cf0` - Initial Configuration Registry**
- Added `supported-configurations.json` with ~280 configuration keys
organized by version (A/B/C)
- Includes `aliases` section mapping primary keys to
deprecated/alternative names
- Includes `deprecations` section with deprecation messages
- Added GitLab CI validation step to ensure file integrity
- Updated one-pipeline lock file to reference validation template

**`70e632e` - Configuration Documentation**
- Added
[supported-configurations-docs.yaml](cci:7://file:///Users/anna.yafi/go/src/github.com/DataDog/dd-trace-dotnet3/tracer/src/Datadog.Trace/Configuration/supported-configurations-docs.yaml:0:0-0:0)
with detailed XML documentation for each configuration key
- Provides human-readable descriptions, default values, and usage
examples
- Includes `<seealso>` references to relevant code classes
- Complements the machine-readable JSON with developer-friendly
documentation
- Enables automated generation of configuration documentation from a
single source

… keys (#7688)

## Context

Part of **Configuration Inversion (Step 2)** - Stack progress:
1. [#7548](#7548) - Add
GitLab step and JSON configuration file
2. **→ [#7688](#7688) -
[Config registry] Reorganize keys, split config keys and platform
keys(this PR)**
3. [#7698](#7698) -
Generate ConfigurationKeys with source generator
4. [#7689](#7689) -
Aliases handling and analyzers
5. [#7697](#7697) -
Replace manual ConfigurationKeys by generated ones in the whole solution
## Summary

Separates platform-specific environment variables into `PlatformKeys`
class and adds Roslyn analyzers to enforce proper usage of configuration
keys throughout the codebase.

## Changes

**Platform Keys Separation:**
- Created `PlatformKeys` class for external platform environment
variables (AWS, Azure, GCP, Kubernetes, CLR Profiler), those that don't
start with DD_ and come from other platforms.
- Updated all references throughout codebase to use `PlatformKeys` for
platform-specific variables
- Keeps `ConfigurationKeys` focused only on Datadog configuration

**Roslyn Analyzers:**
- **DD0007**: Platform key analyzer - Enforces use of `PlatformKeys` for
external platform environment variables
- **DD0008**: ConfigurationBuilder analyzer - Enforces use of
`ConfigurationKeys` or `PlatformKeys` constants in
`ConfigurationBuilder.WithKeys()` calls
- Prevents hardcoded strings and ensures type safety

**Configuration Mapping:**
- Added `configuration_keys_mapping.json` to map environment variable
names to their `ConfigurationKeys` constant names, so that we avoid
renaming hundreds of variables according to automatically source
generated deducted ones.
- Enables preservation of original constant names during refactoring
- Supports source generator integration

**Code Updates:**
- Updated `TracerSettings`, test files, and profiler code to use
`PlatformKeys`
- Replaced manual `ConfigurationKeys` with generated version from
`supported-configurations.json`
- Added missing `DD_TRACE_LOG_PATH` to configuration registry

## Motivation

Ensures clean separation between Datadog and platform configuration by:
- Preventing accidental mixing of platform and Datadog keys
- Enforcing compile-time validation of configuration key usage
- Making it clear which keys are owned by Datadog vs external platforms
- Catching configuration errors at build time instead of runtime

## Validation

- Roslyn analyzers run on every build
- All existing tests pass with updated key references
- Analyzers report clear diagnostic messages for violations

## Related Work

This PR builds on the configuration registry foundation established in
#7548:
- **Commit `2639cf0`** added `supported-configurations.json` with ~280
keys, aliases, deprecations, and GitLab CI validation
- **Commit `70e632e`** added
[supported-configurations-docs.yaml](cci:7://file:///Users/anna.yafi/go/src/github.com/DataDog/dd-trace-dotnet3/tracer/src/Datadog.Trace/Configuration/supported-configurations-docs.yaml:0:0-0:0)
with XML documentation for automated doc generation