Resolve "Create release notes from closed milestone"

  • Add a button "New Release Tag" to milestones/show if the milestone status is closed and no release tag has been created. Screen_Shot_2016-11-26_at_1.13.23_PM Screen_Shot_2016-11-26_at_1.13.38_PM

  • Add a link to milestones/show description with the release tag (if exists) Screen_Shot_2016-11-26_at_1.14.22_PM

  • The tag's description includes the open and closed issues for that milestone. Screen_Shot_2016-11-26_at_1.13.55_PM

Left todo:

  • Add integration specs.
  • When I click to create a new tag but give up and click cancel, it should return to milestone#show instead of tags#index.
  • Replace the inline fields with a Tag model. This wasn't done because would demand a big refactor on other parts of the system, for example in CreateTagService, and I'd never make a big change like this without creating specs (which the time constraints wouldn't allow me to).
  • Even better release notes description formatting.
  • The extras (Like grouping by labels).

Closes #24260 (moved)