R1:cd2f9786bf8e

Shuffle various parts of the config edit UI around

Summary:
Fixes T9339.

- Don't show edit control for locked config at all.
- Don't show a "Cancel" button either.
- Change "Value" label to "Database Value" for non-custom config.
- Highlight effective value.
- Move examples under current state.
- Tweak some formatting.

Test Plan: {F777878}

Reviewers: chad, avivey

Reviewed By: chad, avivey

Subscribers: avivey

Maniphest Tasks: T9339

Differential Revision: https://secure.phabricator.