Adjust content width for User Settings, GPG Keys

What does this MR do?

It adjusts content width for User Settings, GPG Keys when the user has set a fixed layout width in User Settings, Preferences.

Are there points in the code the reviewer needs to double check?

Check if the navigation (nav) also inherits limit-container-width class.

Why was this MR needed?

To keep consistent layout width within User Settings, according to the currently set layout width in User Settings, Preferences.

Screenshots

BEFORE

AFTER