Add API for Issue set Subscription (#8729)

* add issue subscriber API

* subscribers return []user.APIFormat

* add comments

* more meaningfull description

* without "reqToken()" api works ...
 * should be still secure beause ctx.user has to be there or nothing will hapen

* FIX: getIssueWatchers() get only aktive suscriber

* add return avter error on right position

* Revert "FIX: getIssueWatchers() get only aktive suscriber"

This reverts commit 5eca929185.

* Update routers/api/v1/repo/issue.go

Co-Authored-By: guillep2k <18600385+guillep2k@users.noreply.github.com>

* test go linter again

* update swagger

* GetIssueWatchers -> GetIssueSubscribers

part one

Co-Authored-By: guillep2k <18600385+guillep2k@users.noreply.github.com>

* GetIssueWatchers -> GetIssueSubscribers
part two

* Revert "test go linter again"

This reverts commit bab1235622.

* change description for unsubscribe too

* golangci-lint timeout avter 5min

* move issueSubscription to seperate file

* dont create black entitys

* use IsWatching until refactoring

* Update License Info

* better swagger description

* Update .golangci.yml

because functions moved from issue.go to issue_subscription.go

* add IssueWatchList type

* batch tasks

* use e Engien

* add error handling

* error should be the last type when returning multiple items

* short version

* reurn empy UserList instead of nil

models/userlist.go

@@ -8,6 +8,7 @@ import (
 	"fmt"
 
 	"code.gitea.io/gitea/modules/log"
+	api "code.gitea.io/gitea/modules/structs"
 )
 
 //UserList is a list of user.
@@ -93,3 +94,12 @@ func (users UserList) loadTwoFactorStatus(e Engine) (map[int64]*TwoFactor, error
 	}
 	return tokenMaps, nil
 }
+
+//APIFormat return list of users in api format
+func (users UserList) APIFormat() []*api.User {
+	var result []*api.User
+	for _, u := range users {
+		result = append(result, u.APIFormat())
+	}
+	return result
+}