Adds deprecation notice to saved objects API docs

[TinaHeiligers]

Part of #149287
Fix 149988

Updates public API docs listing saved objects APIs that have been deprecated.

Checklist

• Documentation was added for features that require explanation or tutorials

Risk Matrix

Risk	Probability	Severity	Mitigation/Notes
High number of support cases and/or discuss issues asking for more alternative APIs than just for data views	medium	medium	We plan to add more alternatives as public APIs become available

For maintainers

• This was checked for breaking API changes and was labeled appropriately No breaking changes since these APIs are still available as deprecated

[github-actions]

Documentation preview:

• ✨ Changed pages

[elasticmachine]

Pinging @elastic/kibana-core (Team:Core)

[TinaHeiligers]

Preview of the SO APIs list:

[KOTungseth]

LGTM! Do we know the version for when we plan to remove the APIs? If we do, can we include it?

[TinaHeiligers]

Do we know the version for when we plan to remove the APIs?

Right now, we don't. Removing them entirely depends on when consumers no longer use these and we can guarantee there are alternatives. As soon as we know when they'll be removed, we'll add the version.