Support running user-defined hooks through sudo

[guillep2k]

• Gitea version (or commit ref): 1.10.0

Description

Currently git hooks defined by the users are ran with the same credentials as gitea. It would be more secure if the admin could choose a different set of credentials (e.g. through sudo) to run these scripts. It may even be possible to customize which credentials on a repo-owner basis.

This way admins can ease up a little when giving hook creation permissions.

Additionally, the environment variables should be configurable, to avoid passing info that is not required by that particular owner.

[guillep2k]

From @zeripath:

It's worth being aware that our docker friends who like to use environment variables - as it currently stands the internal ssh and http system leaks that whole environment to the hook commands - openSSH may be configured differently.