Migration for audit events partitioning

What does this MR do?

This adds a migration to use the migration helper introduced in !32240 (merged) and create a partitioned table for audit events.

With an intention to fix the broken specs around Geo (see !32240 (comment 345561116)), we are putting partitions into a separate schema partitions. This is good from a convenience point of view where we don't clutter the public schema with a lot of identical looking tables.

I don't know if Geo plays nicely with that, though or if there's an expectation everything resides in public.

❗ Pending: We need to verify this works fine with a Geo setup.

The original change created partitions in public. This lead to https://gitlab.com/gitlab-org/gitlab/-/jobs/559733644 blowing up.

Now my suspicion is that we only need to expose tables in public through FDW and that's still fine before and after this change. We never access partitions schema directly, also not through FDW.

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content

Availability and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• Tested in all supported browsers
• Informed Infrastructure department of a default or new setting change, if applicable per definition of done

Security

If this MR contains changes to processing or storing of credentials or tokens, authorization and authentication methods and other items described in the security review guidelines:

• Label as security and @ mention @gitlab-com/gl-security/appsec
• The MR includes necessary changes to maintain consistency between UI, API, email, or other methods
• Security reports checked/validated by a reviewer from the AppSec team