Launch Gitea with custom UID/GID for 'git' user (fixes #2286)

[HenrikBengtsson]

Fixes #2286

[sapk]

LGTM

[lunny]

@sapk how did you test that?

[sapk]

This method is used other image. You can test it (i haven't done it) by setting env variable at docker run. We could maybe provide a docker-copose.yml file now that the container is configurable by env variable.

Another solution for this problem, is to not create the user in the image (Dockerfile) and do a useradd with fixed UID and GID at startup of container.

[codecov-io]

Codecov Report

Merging #2791 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #2791   +/-   ##
=======================================
  Coverage   26.85%   26.85%           
=======================================
  Files          89       89           
  Lines       17607    17607           
=======================================
  Hits         4728     4728           
  Misses      12193    12193           
  Partials      686      686

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[bkcsoft]

LGTM (Seen this in other docker images as well)

[HenrikBengtsson]

Not a formal unit test, but see #2286 (comment) for a manual test that shows how both UID and GID are modified.

[bkcsoft]

@HenrikBengtsson Unit-testing this would be very hard TBH. Since that would require the contributor to have docker installed. And in out CI it would mean running docker-in-docker which is a pain 😞