chore: Update MonitorLockedTablesWorker specs to handle sec connection

What does this MR do and why?

chore: Update MonitorLockedTablesWorker specs to handle sec connection.

For context on what this worker is, see #413656 (closed) but tl;dr is we use this table to ensure we are not writing to a database's tables that do not correspond to that databases gitlab_schema; i.e. ci tables are locked on gitlab_main and vice-versa.

This MR adds support for gitlab_sec as well and a specific spec to describe the multi-database interactions.

See FAQ for overall sec-decomposition effort &13043

References

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• Relates to Resolve incorrect connection usage raised in sp... (#501606 - closed)

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