In some projects it may be desirable for the trailer to contain a link to
the Gerrit review page so that it is convenient to access the review page
starting from the commit message. The Link trailer is a standard trailer
used for inserting links in the commit message, which has been adopted by
the Linux kernel among other projects. For example, the Linux kernel has a
policy about linking to the mailing list archive with Link trailers:
https://www.kernel.org/doc/html/latest/maintainer/configure-git.html#creating-commit-links-to-lore-kernel-org
This change makes Gerrit interoperate well with the Link trailer. Specifically,
it teaches the Gerrit server to recognize trailers of the form:
Link: https://gerrit-review.googlesource.com/id/I78e884a944cedb5144f661a057e4829c8f84e933
as well as the existing Change-Id trailer, teaches the server to recognize
/id/ as a search prefix for change IDs and modifies the commit-msg hook
to optionally add a Link trailer (using a server URL provided in the
property gerrit.reviewUrl) instead of the Change-Id trailer.
Change-Id: I78e884a944cedb5144f661a057e4829c8f84e933
8cab93302d