Process issue ids from pull request comment mentions

[eheimbuch]

Proposed changes

Trigger comment handler on SCM-Manager pull request comment events to handle issue ids inside comments.

Your checklist for this pull request

• [x] PR is well described and the description can be used as commit message on squash
• [x] Related issues linked to PR if existing and labels set
• [x] Target branch is not master (in most cases develop should bet the target of choice)
• [x] Code does not conflict with target branch
• [x] New code is covered with unit tests

Checklist for branch merge request (not required for forks)

• [ ] Branch is green/blue on Jenkins
• [ ] Quality Gate passed on SonarQube