Draft: Add basic logic to get PWA working
What does this MR do and why?
This WIP MR adds very basic PWA support to GitLab. I'm not a FE expert so some of the changes make break things and some definitely need to be moved to a more appropriate place.
Screenshots or screen recordings
Applying the diff as a patch to a production, personal GitLab instance running under HTTPS (HTTPS is critical for PWA to work) works and is detected as PWA installable by Chrome's lighthouse report:
Related to #18456
Edited by Ash McKenzie