Implement Users::BuildService

Closes #30349

See merge request !10675

Expand components version specification format to allow branches

Closes gitaly#183

See merge request !10610

Currently we specify versions for Gitlab-Shell, Workhorse and Gitaly
using version strings, to which we prepend 'v' and assume are tags.
These changes allow branches or tags with other name formats to be
specified by prepending '=' to the version string (á la govendor).

We also simplify the process to reset to the given version (now a
branch or tag): Right now there's a check to supposedly try to avoid
fetching from the remote the version if it already exist locally. But
the previous logic already clones if the directory doesn't exist or
fetches if it does, so this check is pointless. We can safely assume the
version exists once we get to the reset stage.

Fix appending state to issuable references

Closes #30874

See merge request !10683

After Trace#limit, we seek to the next line in case

Closes #30796

See merge request !10681

Closes #30874.
Ignore nodes with no children.
Append directly to the node instead of the last child of the node
to avoid inheriting formatting from the last child

then it's fine to skip the first line because
it won't be very noticeable

of breaking ANSI sequence or Unicode