Adds a name filter to the API for GetMilestoneList

Includes a small refactor: merge GetMilestones and GetMilestonesByRepoID

Close #12260

Needed for https://gitea.com/gitea/go-sdk/issues/383 and https://gitea.com/gitea/tea/pulls/149

* API allow to create closed milestones

* set CloseDate too

Co-authored-by: Lauris BH <lauris@nix.lv>
Co-authored-by: techknowlogick <techknowlogick@gitea.io>

* Fix milestone API state parameter unhandled

* Fix test