Backport #8901
In investigating #7947 it has become clear that the storage component of go-git repositories needs closing.
This PR adds this Close function and adds the Close functions as necessary.
In TransferOwnership the ctx.Repo.GitRepo is closed if it is open to help prevent the risk of multiple open files.
Fixes#7947
* extract actions on new pull request from models to pulls service
* improve code
* move code.gitea.io/gitea/modules/pull to code.gitea.io/gitea/services/pull
* fix fmt
* Rename pulls.go to pull.go
* refuse merge until ci successfully
* deny merge request when required status checkes not succeed on merge Post and API
* add database migration for added columns on protected_branch
* fix migration
* fix protected branch check bug
* fix protected branch settings
* remove duplicated code on check pull request's required commit statuses pass
* remove unused codes
* fix migration
* add newline for template file
* fix go mod
* rename function name and some other fixes
* fix template
* fix bug pull view
* remove go1.12 wrong dependencies
* add administrator bypass when protected branch status check enabled
* fix bug
* improve the codes
zeripath
Elias Norberg
Lunny Xiao