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

* move mirror to a standalone package

* fix mirror address in template

* fix tests

* fix lint

* fix comment

* fix tests

* fix tests

* fix vendor

* fix fmt

* fix lint

* remove wrong file submitted

* fix conflict

* remove unrelated changes

* fix go mod

* fix tests

* clean go mod

* make vendor work

* make vendor work

* fix tests

* remove duplicated test

* extract actions on deletereleasebyid from models to release service

* fix tests

* move create release from models to a standalone package

* fix lint

* fix comment year

* fix lint

* fix lint

* fix package import name

* fix vendor

* fix go mod

* some refactors

* fix vendor

* use go1.12 make vendor

* fix vendor

Whenever we assign a value to err, check for it being nil.

* fix bug conflict between SyncReleasesWithTags and InsertReleases

* fix tests

* fix fmt

* add migrations

* fix package dependency

* fix lints

* implements migrations except pull requests

* add releases

* migrating releases

* fix bug

* fix lint

* fix migrate releases

* fix tests

* add rollback

* pull request migtations

* fix import

* fix go module vendor

* add tests for upload to gitea

* more migrate options

* fix swagger-check

* fix misspell

* add options on migration UI

* fix log error

* improve UI options on migrating

* add support for username password when migrating from github

* fix tests

* remove comments and fix migrate limitation

* improve error handles

* migrate API will also support migrate milestones/labels/issues/pulls/releases

* fix tests and remove unused codes

* add DownloaderFactory and docs about how to create a new Downloader

* fix misspell

* fix migration docs

* Add hints about migrate options on migration page

* fix tests

* move code.gitea.io/git to code.gitea.io/gitea/modules/git

* fix imports

* fix fmt

* fix misspell

* remove wrong tests data

* fix unit tests

* fix tests

* fix tests

* fix tests

* fix tests

* fix tests

* enable Debug to trace the failure tests

* fix tests

* fix tests

* fix tests

* fix tests

* fix tests

* comment commit count tests since git clone depth is 50

* fix tests

* update from code.gitea.io/git

* revert change to makefile

This bug was being caused by an error in the logic in `release.go`.
Credit to @yasuokav for tracing the root of the issue.

Fixes: #5192.

* fix release creation via API

* fix release create tests