Add webhook support for automatic MR review in the right channel

[M0nkeySan]

Current Behavior

Currently, merge requests can only be added to Slack channels manually using the review command. This requires manual intervention for each MR that needs to be tracked in Slack.

When a MR is opened by an automation, like renovate-bot, the MR is not added in the slack channel.

Proposed Enhancement

Add support for GitLab webhooks to automatically assign merge requests to configured Slack channels based on MR labels. This would enable automatic tracking of MRs in relevant channels as soon as they are created.

The idea would be to create a dedicated label homer-review which trigger the automation on homer side or not.

How

The code which handle the webhook from the MR is located in mergeRequestHookHandler.ts.

The needed changes are :

1. Add a handler for the open action, check if the labels array contains homer-review
2. Search if the project_id field is linked to 1 or more channels in the database.
3. Build the review message with buildReviewMessage
4. Add the review to the channels addReviewToChannel

[greg0ire]

This would enable automatic tracking of MRs in relevant channels as soon as they are created.

I think maybe this should be avoided. I like to avoid notifying my colleagues until I've reviewed the MR myself, have a green pipeline, sometimes I even run tests on integration before that. I would be favorable to something that triggers auto-tracking when the PR is marked as "ready for review" and has at least one reviewer assigned.