* Rename `datasource` saved object to `package_config` (SO type `ingest-datasource` to `ingest-package-config`) and adjust mappings:

- Remove unused `processors` field on input & stream levels
- Remove unnecessary `enabled` field on package config & input levels
- Rename `agent_stream` field to `compiled_stream`
- Reorder other fields so that important fields are closer to top & similar fields are grouped together

Also,
- Remove 7.9.0 migrations as we are not supporting an upgrade path from experimental to beta release

* Pluralize `ingest-package-configs` for consistency

* Rename `Datasource`-related types to `PackageConfig`, update all references (does not include actual type definition changes yet)

* Rename `Datasource` schemas and rest spec typings to `PackageConfig` (does not include actual schema changes yet)

* Change `datasources` on agent config typings and schemas to `package_configs` and update all references

* Add back `enabled` field on package config and input levels. They are needed for current & future UI features. Also:

- Match types and schemas with saved object mappings (`agent_stream` to `compiled_stream`, removal of `processors`)
- Set `namespace` to be a required property on agent config and package config types, add validation support for it on UI

* Rename server-side datasource references in file names, variable names, and routes

* Update spec file and schema file

* Update doc wording

* Rename all instances of datasource in file paths and variable names on client sides, and for Endpoint too

* Minor copy adjustments, fix i18n check

* Replace datasource references in tests and fixtures; remove unused `ingest/policies` es archiver data

* Fix tests

* Fix test field name

* Fix test fixtures fields again

* Fix i18n
# Conflicts:
#	x-pack/plugins/translations/translations/ja-JP.json
#	x-pack/plugins/translations/translations/zh-CN.json