Add Merge Request filter for draft similar to WIP

[javydreamercsw]

Recently Draft was introduced to Gitlab but there is no way to filter for it like WIP currently.

new MergeRequestFilter()
                              .withProjectId(project.getId())
                              .withState(MergeRequestState.OPENED)
                              .withWip(false)

Ideally it would be similar:

new MergeRequestFilter()
                              .withProjectId(project.getId())
                              .withState(MergeRequestState.OPENED)
                              .withWip(false)
                              .withDraft(false)