Reconfigure the Geo tracking database pool size when running as Sidekiq

What does this MR do?

Modify the Sidekiq initializer so it set the connection pool size to the Geo tracking database in the same way as it does for the main database

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

We don't need to call establish_connection for this to work, so I've left that out here.

Why was this MR needed?

Without it, the pool size needs to be set for maximum sidekiq concurrency. However, the unicorns respect this value too so this quickly multiplies into hundreds or thousands of database connections at the postgres server.

Screenshots (if relevant)

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• 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

What are the relevant issue numbers?

Closes #3809 (closed)