Add the ability to pin Issues (#24406)

This adds the ability to pin important Issues and Pull Requests. You can
also move pinned Issues around to change their Position. Resolves #2175.

## Screenshots

![grafik](https://user-images.githubusercontent.com/15185051/235123207-0aa39869-bb48-45c3-abe2-ba1e836046ec.png)

![grafik](https://user-images.githubusercontent.com/15185051/235123297-152a16ea-a857-451d-9a42-61f2cd54dd75.png)

![grafik](https://user-images.githubusercontent.com/15185051/235640782-cbfe25ec-6254-479a-a3de-133e585d7a2d.png)

The Design was mostly copied from the Projects Board.

## Implementation
This uses a new `pin_order` Column in the `issue` table. If the value is
set to 0, the Issue is not pinned. If it's set to a bigger value, the
value is the Position. 1 means it's the first pinned Issue, 2 means it's
the second one etc. This is dived into Issues and Pull requests for each
Repo.

## TODO
- [x] You can currently pin as many Issues as you want. Maybe we should
add a Limit, which is configurable. GitHub uses 3, but I prefer 6, as
this is better for bigger Projects, but I'm open for suggestions.
- [x] Pin and Unpin events need to be added to the Issue history.
- [x] Tests
- [x] Migration

**The feature itself is currently fully working, so tester who may find
weird edge cases are very welcome!**

---------

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

routers/api/v1/api.go

@@ -967,6 +967,7 @@ func Routes(ctx gocontext.Context) *web.Route {
 				m.Group("/issues", func() {
 					m.Combo("").Get(repo.ListIssues).
 						Post(reqToken(auth_model.AccessTokenScopeRepo), mustNotBeArchived, bind(api.CreateIssueOption{}), repo.CreateIssue)
+					m.Get("/pinned", repo.ListPinnedIssues)
 					m.Group("/comments", func() {
 						m.Get("", repo.ListRepoIssueComments)
 						m.Group("/{id}", func() {
@@ -1047,6 +1048,12 @@ func Routes(ctx gocontext.Context) *web.Route {
 							Get(repo.GetIssueBlocks).
 							Post(reqToken(auth_model.AccessTokenScopeRepo), bind(api.IssueMeta{}), repo.CreateIssueBlocking).
 							Delete(reqToken(auth_model.AccessTokenScopeRepo), bind(api.IssueMeta{}), repo.RemoveIssueBlocking)
+						m.Group("/pin", func() {
+							m.Combo("").
+								Post(reqToken(auth_model.AccessTokenScopeRepo), reqAdmin(), repo.PinIssue).
+								Delete(reqToken(auth_model.AccessTokenScopeRepo), reqAdmin(), repo.UnpinIssue)
+							m.Patch("/{position}", reqToken(auth_model.AccessTokenScopeRepo), reqAdmin(), repo.MoveIssuePin)
+						})
 					})
 				}, mustEnableIssuesOrPulls)
 				m.Group("/labels", func() {
@@ -1109,6 +1116,7 @@ func Routes(ctx gocontext.Context) *web.Route {
 				m.Group("/pulls", func() {
 					m.Combo("").Get(repo.ListPullRequests).
 						Post(reqToken(auth_model.AccessTokenScopeRepo), mustNotBeArchived, bind(api.CreatePullRequestOption{}), repo.CreatePullRequest)
+					m.Get("/pinned", repo.ListPinnedPullRequests)
 					m.Group("/{index}", func() {
 						m.Combo("").Get(repo.GetPullRequest).
 							Patch(reqToken(auth_model.AccessTokenScopeRepo), bind(api.EditPullRequestOption{}), repo.EditPullRequest)
@@ -1186,6 +1194,7 @@ func Routes(ctx gocontext.Context) *web.Route {
 				m.Get("/issue_config/validate", context.ReferencesGitRepo(), repo.ValidateIssueConfig)
 				m.Get("/languages", reqRepoReader(unit.TypeCode), repo.GetLanguages)
 				m.Get("/activities/feeds", repo.ListRepoActivityFeeds)
+				m.Get("/new_pin_allowed", repo.AreNewIssuePinsAllowed)
 			}, repoAssignment())
 		})