Add API for Issue set Subscription (#8729)

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 5eca9291858a821981992b0aaa38cef610d84bca.

* 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 bab12356227e44334de113b76f12099de0b8aaa6.

* 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