save new comment on issue

[SimonLab]

As a user I want new comments on an issue to be saved So that I can start a history backup of all the comments on the issue

• [x] Catch "new comment" webhook notificiation
• [x] Get the issue from Postgres linked to the comment. Repo.get_by!(Issue, issue_id: issue_id)
• [x] Build a new association with the comment params and the issue by using build_assoc
• [x] Save the new issue/comment with Repo.update!
• [x] Get the s3 content linked to the issue
• [x] Add a new version: comment in the file content and save the file back to S3

[nelsonic]

done. 🎉 (nice work @SimonLab!)