[FE] Add false positive warning

Summary

In #508941 (closed) we discuss a potential false positive edge case where dormant members may be removed that have not been dormant for the full 90 day period.

This is a short-lived problem, but in the mean time we need to add a warning to users about it.

Proposal

Update the hint text for the remove_dormant_members namespace setting to inform / direct users to the docs, similar to:

Exact content to be confirmed in this thread