RFR: 1936: IssueCommand would change pr title in GitLab

[Zhao Song]

In GitLab, when a user wants to create a PR in draft mode, they need to include the prefix "Draft: " before the title(Checked the GitLab Document, "WIP" is already deprecated and removed). However, if the user wants to use the "/issue" command to add another issue to this PR, the pr bot will not be able to parse the issue within the PR title. Therefore, the bot will modify the PR title to match the new issue the user wants to add, resulting in the removal of the draft state of the PR.

To resolve this issue, we need to remove the draft prefix before trying to parse the title issue.

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

Commit messages:
 - SKARA-1936

Changes: https://git.openjdk.org/skara/pull/1528/files
 Webrev: https://webrevs.openjdk.org/?repo=skara&pr=1528&range=00
  Issue: https://bugs.openjdk.org/browse/SKARA-1936
  Stats: 6 lines in 1 file changed: 5 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/skara/pull/1528.diff
  Fetch: git fetch https://git.openjdk.org/skara.git pull/1528/head:pull/1528

PR: https://git.openjdk.org/skara/pull/1528