- Fixes the alignment of the various custom headers tables
- Fixed dark mode background
- Added tooltip to the custom header delete button
- Changes the new header row creation to a manual process rather than
an automated one
- Revises the streaming destinations count to be clear on what is
being counted
- Changed the position of the add form button to be on the same
visual line as the streaming destinations count
- Update the docs to match the UI changes

Signed-off-by: Robert Hunt <rhunt@gitlab.com>

Changelog: changed
EE: true
MR: !93183