Add option to close issues via commit on a non master branch (#5992)

* fixes #5957

* add tests to make sure config option is respected

* use already defined struct

* - use migration to make the flag repo wide not for the entire gitea instance
Also note that the config value can still be set so as to be able to control the value for new repositories that are to be created

- fix copy/paste error in copyright header year and rearrange import

- use repo config instead of server config value to determine if a commit should close an issue

- update testsuite

* use global config only when creating a new repository

* allow repo admin toggle feature via UI

* fix typo and improve testcase

* fix fixtures

* add DEFAULT prefix to config value

* fix test

docs/content/doc/advanced/config-cheat-sheet.en-us.md

@@ -65,6 +65,7 @@ Values containing `#` or `;` must be quoted using `` ` `` or `"""`.
 - `ACCESS_CONTROL_ALLOW_ORIGIN`: **\<empty\>**: Value for Access-Control-Allow-Origin header,
    default is not to present. **WARNING**: This maybe harmful to you website if you do not
    give it a right value.
+- `DEFAULT_CLOSE_ISSUES_VIA_COMMITS_IN_ANY_BRANCH`:  **false**: Close an issue if a commit on a non default branch marks it as closed.
 
 ### Repository - Pull Request (`repository.pull-request`)
 - `WORK_IN_PROGRESS_PREFIXES`: **WIP:,\[WIP\]**: List of prefixes used in Pull Request