FE: Provide an admin setting to automate deactivation of dormant users

Description

In GitLab Self-Managed (TODO - is this correct?), if a user did not sign in, or has had any activity in 90 days, the administrator will be granted the option to manually deactivate them (docs about this here).

Manually deactivating dormant users can be cumbersome.

This issue deals with adding an admin setting that if toggled on will have the effect of automatically deactivating the dormant users (users with no log-in or activity for the past 90 days).

Designs

Link with UX discussion: #282537[deactive_dormant_users.png]

Setting location

Inside of Admin > Settings > Account and Limit, right after the New users set to external section.

Text

• Title: Dormant users
• Label: Deactivate dormant users after 90 days of inactivity. Users can return to active status by logging into their account. While inactive, a user will not be counted as an active user in the instance. More information
• Help link URL: This URL will be available after the docs MR will get merged

Related Back-End issue

#211754 (closed)