Adjust content width for User Settings, Pipeline quota

What does this MR do?

It adjusts content width for User Settings, Pipeline quota 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?

No.

Why was this MR needed?

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

What are the relevant issue numbers?

No relevant issues but similar changes will be have been merged to CE, too. See https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/16093