https://gitlab.com/gitlab-org/build/CNG/-/merge_requests/1546
introduced an additional build stage to generating the Bootsnap cache
for a standard GitLab startup using Docker Compose. However, we can
avoid this Docker Compose step if we simply compile all Ruby code
`/srv/gitlab` and use the `--gemfile` Bootsnap argument
(https://github.com/Shopify/bootsnap/blob/master/README.md#precompilation).
While this increases the total size of the Bootsnap cache from 146 MB
to 267 MB, this guarantees that there will be no cache misses and
speeds up the build.

Relates to https://gitlab.com/gitlab-org/build/CNG/-/merge_requests/1743

Changelog: changed