Autocomplete disabled for many `gl.GLForm`

https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/11278 disabled the autocomplete for all the gl.GLForm instances across GitLab which isn't desired for many places.

• Many gl.GLForm instances in dispatcher.js
  • Milestone creation/edit/update, /gitlab-org/gitlab-ce/milestones/new
  • New/Edit Issue (covered elsewhere but should be true)
  • New/Edit MR (covered elsewhere but should be true)
  • New Tag /gitlab-org/gitlab-ce/tags/new
  • Snippets should have explicit false. Snippet comments being fixed up here https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/12108
  • Edit Release, /gitlab-org/gitlab-ce/tags/v8.15.3/release/edit
  • Wiki editing, /gitlab-org/gitlab-ce/wikis/...
• notes.js: Fixed in https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/12106
• Issue description: Fixed in https://gitlab.com/gitlab-org/gitlab-ce/commit/e20654fcc33ad4e7df0e5da1112c33f99d4630b7, whole MR: https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/11322