Resolve "mysql-only installation from source broken: Gem::LoadError: pg is not part of the bundle"

What does this MR do?

Fixes two initializers so that they don't assume the pg or peek-pg gems are installed in various scenarios.

Are there points in the code the reviewer needs to double check?

Why was this MR needed?

Install-from-source mysql users encountering problems

Screenshots (if relevant)

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Documentation created/updated
• API support added
• Tests added for this feature/bug
• Review
  • Has been reviewed by Backend
• Conform by the merge request performance guides
• Conform by the style guides
• Squashed related commits together
• Internationalization required/considered
• End-to-end tests pass (package-qa manual pipeline job)

What are the relevant issue numbers?

Closes #42239 (closed)