Add script to loop and query multiple dbs for stat data

What does this MR do and why?

Collect data for a variety of metrics on every database (primary and replica, main, ci, etc), every 5 seconds in a loop, for 5 minutes or until cancelled:

• Table sizes for all relations
• Snapshots of pg_stat_activity
• Snapshots of pg_locks, taken at the same time as pg_stat_activity so data can be correlated.
• Snapshots of pg_stat_user_tables, pg_stat_user_indexes, pg_statio_user_tables, pg_statio_user_indexes

References

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• #510170 (closed)

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