Migrate es-archiver documents data from ES to SO format and provide associated tooling

[pgayvallet]

Now that SavedObjects types can be registered from NP, the current implementation of the es-archiver has no way to be aware of all the registered SO types, and therefor can no longer instantiate a KibanaMigrator on it's own to perform the migration of it's documents after a load action.

In #55860, we decided to implements a 'temporary' /migrate savedobject endpoint to replace the migration that was done in src/es_archiver/lib/indices/kibana_index.ts.

The consensus on the long term solution would be to keep the archiver data up to date and convert it to saved object format to avoid using raw ES apis, and load them using the SO endpoints (create) instead.

Do achieve this, we need to:

• Converts all the existing document data used by the es-archiver (example: test/functional/fixtures/es_archiver) from ES raw format to SO format
• Adapt the es-archiver load action to properly handle the new format, and use the kbnClient.savedObjects to load the SO into elastic.
• get rid of the manual migration
• Provides tooling to allow plugin developers to create, migrate and maintains any additional test data they would need to use for testing.

[elasticmachine]

Pinging @elastic/kibana-platform (Team:Platform)

[pgayvallet]

We now have the kbnArchiver, and QA has been working on migrating the data sets from esArchiver to this new tool, so I'll consider this done or superseded.