Set the user who applies suggestion as the commit author

Before:

For a single suggestion:

- The author of the suggestion note is set as the author
- The user who applies the suggestion is the committer

For batch suggestions:

- The user who applies the suggestion is the author and committer

Now:

For signle and batch suggestions:

- The user who applies the suggestion is the author and committer

In a separate commit/MR an option to provide co-authors will be
introduced.

When commit signing is enabled, the committer will be GitLab