Add support for Gitlab Todo

There is quite useful tool like Gitlab Todo. Quotation form documentation:

• An issue or merge request is assigned to you.
• A merge request review is requested.
• You’re mentioned in the description or comment of an issue, merge request, or epic.
• You’re mentioned in a comment on a commit or design.
• The CI/CD pipeline for your merge request fails.
• An open merge request cannot be merged due to conflict...
• ...etc

It is a useful start point for working with MR's.

There is a documentation page for Todo's API.

There is such a feature in lab.

P.S. It looks like Github doesn't have something like Gitlab Todo.