More details about troubleshooting inactive replication slot

What does this MR do?

When a postgresql replication slot is not active, one should not just delete it. Instead ask themselves, should it be active and if so, why isn't it active.

If they intent to not use it, they can remove it.

Why was this MR needed?

Confusion in a customer ticket: ZD

Screenshots (if relevant)

gitlabhq_production=# SELECT * FROM pg_replication_slots;
     slot_name     | plugin | slot_type | datoid | database | active | active_pid | xmin | catalog_xmin | restart_lsn | confirmed_flush_lsn 
-------------------+--------+-----------+--------+----------+--------+------------+------+--------------+-------------+---------------------
 secondary_example |        | physical  |        |          | f      |            |      |              | 52/B8000168 | 
(1 row)

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 UX
  • [-] Has been reviewed by Frontend
  • Has been reviewed by Backend
  • [-] Has been reviewed by Database
• Conform by the merge request performance guides
• Conform by the style guides
• Squashed related commits together
• [-] Internationalization required/considered
• [-] If paid feature, have we considered GitLab.com plan and how it works for groups and is there a design for promoting it to users who aren't on the correct plan

What are the relevant issue numbers?

/

cc @ckatanda