Add review request api (#11355)

* Add review request api

* add : POST /repos/{owner}/{repo}/pulls/{index}/requested_reviewers
* Remove : DELET /repos/{owner}/{repo}/pulls/{index}/requested_reviewers
* fix some request review bug
* block delet request review by models/DeleteReview()

Signed-off-by: a1012112796 <1012112796@qq.com>

* make fmt

* fix bug

* fix test code

* fix typo

* Apply suggestion from code review @jonasfranz

* fix swagger ref

* fix typo

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

* fix comment

* Change response message

* chang response so some simplfy

* Add ErrIllLegalReviewRequest
fix some nits

* make fmt

* Apply suggestions from code review

Co-authored-by: silverwind <me@silverwind.io>

* * Add team support
* fix test
* fix an known bug

* fix nit

* fix test

* Apply suggestions from code review

Co-authored-by: zeripath <art27@cantab.net>

* update get api and add test

Co-authored-by: Lauris BH <lauris@nix.lv>
Co-authored-by: silverwind <me@silverwind.io>
Co-authored-by: zeripath <art27@cantab.net>

routers/api/v1/api.go

@@ -827,7 +827,9 @@ func RegisterRoutes(m *macaron.Macaron) {
 									Get(repo.GetPullReviewComments)
 							})
 						})
-
+						m.Combo("/requested_reviewers").
+							Delete(reqToken(), bind(api.PullReviewRequestOptions{}), repo.DeleteReviewRequests).
+							Post(reqToken(), bind(api.PullReviewRequestOptions{}), repo.CreateReviewRequests)
 					})
 				}, mustAllowPulls, reqRepoReader(models.UnitTypeCode), context.ReferencesGitRepo(false))
 				m.Group("/statuses", func() {