PgBouncer docs need to mention backups

What does this MR do?

The backup/restore docs detail that steps are needed for PgBouncer. Added some more details on symptoms customers may see (slack - internal link)

The docs for setting up PgBouncer do not mention the need to reconfigure backups. Add short sections with the 'why' and 'where'.

Linked secrets doctor into restore steps.

Sequenced warnings into backup steps so they are in line with those tasks.

Related issues

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