DM-52449: Add gaia_dr2 for internal testing.

[ctslater]

Checklist

When making changes to YAML files in the schemas directory:

• If applicable, incremented the schema version number, following the guidelines in the contribution guide
• Referred to the documentation on specific schemas for additional versioning information, change constraints, or tasks that may need to be performed, based on which schema is being updated
• Ran Jenkins
• Added a news fragment describing the changes

[JeremyMcCormick]

@ctslater I assume this will never be merged and is only here for testing?

In that case, can it be marked as a draft and/or with a clear "do not merge" notice?

[gpdf]

I understand that this is going to be merged but only deployed to data-int (via build-all magic).

[JeremyMcCormick]

I understand that this is going to be merged but only deployed to data-int (via build-all magic).

I would think it should not be shown in the schema browser (?).