RFR: forge: improve GitLabRepository::commitWithComment

[Erik Helin]

Hi all,

please review this patch that improves the method `GitLabRepository::commitWithComment`. The problem is that GitLab's search API isn't really up to par (cannot handle square brackets in search query) and the search API is also going in away from GitLab CE in 13.9. This patch implements a simple search, just iterating backwards over the most recent commits, searching for the given title. The results are cached in-memory to speed up future searches.

Testing:
- [x] Manual testing on Linux x64 using `git-skara debug commit-comments`

Thanks,
Erik

-------------

Commit messages:
 - forge: improve GitLabRepository::commitWithComment

Changes: https://git.openjdk.java.net/skara/pull/1020/files
 Webrev: https://webrevs.openjdk.java.net/?repo=skara&pr=1020&range=00
  Stats: 58 lines in 1 file changed: 30 ins; 8 del; 20 mod
  Patch: https://git.openjdk.java.net/skara/pull/1020.diff
  Fetch: git fetch https://git.openjdk.java.net/skara pull/1020/head:pull/1020

PR: https://git.openjdk.java.net/skara/pull/1020