feat: make gitlab integration plugins

[k4black]

Make the following plugins and tests for them:

• validate gitlab MR with checklist. Fail plugin run if some check failed. Return it as plugin output, not in MR.
• Collect score from gitlab MR: 1. search for a comment "Place your score here:", if not exist - create one. 2. Search for a comment with score by admin of A gitlab group (teachers). Return it as plugin output.

See course-template .checker file to see approximate usage