Add CommitID to CreateMergeRequestDiscussionOptions
Add CommitID to CreateMergeRequestDiscussionOptions

While not explicitly stated in the documentation [1] the commit_id field
must be specified when creating a MR discussion (aka thread) with comments
on a commit.

Add a CommitID to the CreateMergeRequestDiscussionOptions struct.

[1] https://docs.gitlab.com/ee/api/discussions.html#create-new-merge-request-thread
Signed-off-by: Prarit Bhargava <fe4655370dc87a32329d591d6e8472329333dfad@redhat.com>

xanzy/go-gitlab