Move issues from `feature request` to `feature proposal`

• Edit issues with feature request tag to contain the feature proposal tag
• Remove feature request tag

• https://gitlab.com/gitlab-org/gitlab-ce/issues?label_name=feature+request
• https://gitlab.com/gitlab-org/gitlab-ce/issues?label_name=feature+proposal

mentioned in issue #4038 (closed)

Ok cleaned up, we currently have 83 issues tagged with feature proposal :)

Status changed to closed

Awesome @axil