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>

models/fixtures/review.yml

@@ -86,3 +86,22 @@
   official: true
   updated_unix: 946684815
   created_unix: 946684815
+
+-
+  id: 11
+  type: 4
+  reviewer_id: 0
+  reviewer_team_id: 7
+  issue_id: 12
+  official: true
+  updated_unix: 1602936509
+  created_unix: 1602936509
+
+-
+  id: 12
+  type: 4
+  reviewer_id: 1
+  issue_id: 12
+  official: true
+  updated_unix: 1603196749
+  created_unix: 1603196749