When helm input method generates consumer identities for OCI repository
URLs (oci://), it now returns type "OCIRegistry" instead of
"HelmChartRepository". This allows the OCI credential repository plugin
to match and resolve credentials correctly.

After issue open-component-model#786 fix, the OCI credential repository plugin only handles
OCIRegistry type, which caused credential lookup to fail for OCI-hosted
Helm charts. This change aligns the consumer identity type with the
actual protocol.

Non-OCI URLs (http://, https://) continue using HelmChartRepository
type for backward compatibility.

Refs: open-component-model/ocm-project#967
Signed-off-by: Fabian Burth <fabian.burth@sap.com>

## Summary

- Fix consumer identity type for OCI-based Helm repositories to return
`OCIRegistry` instead of `HelmChartRepository` when the URL uses
`oci://` scheme
- Add support for `accessToken` credential mapping for OCI registries
(token is mapped to password for basic auth when password is not
present)

This resolves credential lookup failures for Helm charts hosted on OCI
registries after issue #786 fix removed the OCI fallback for
`AnyConsumerIdentityType`.

## Changes

1. **Consumer identity type fix** (`bindings/go/helm/input/method.go`,
`bindings/go/helm/access/access.go`):
- Detect `oci://` scheme and return `OCIRegistry` consumer identity type
- Non-OCI URLs (http://, https://) continue using `HelmChartRepository`
for backward compatibility

2. **Credential mapping**
(`bindings/go/helm/internal/download/download.go`):
- When `password` is not present but `accessToken` is, map the token to
password for basic auth
- Enables token-based authentication with OCI registries like GitHub
Container Registry

## Test plan

- [x] Unit tests added for OCI scheme detection in both input and access
methods
- [x] Existing tests updated to expect `OCIRegistry` type for OCI URLs
- [x] All helm module tests pass
- [x] Linter passes
- [x] compiled the cli with go work and tested it against a private oci
helm chart

Closes open-component-model/ocm-project#967

---------

Signed-off-by: Fabian Burth <fabian.burth@sap.com>