Create a service method to fetch the comments made by a user

Summary

Create a service method to retrieve all comments made by one user on merge requests and issues within a certain time stamp.

Checklist

• retrieve comments and discussion threads per project
• retrieve comments and discussion threads per group

Implementation details

The GitLab API makes a distinction between the comments made at the root of an issue / merge request and discussion threads. Both types of comments should be taken into account in the implementation.