This reduces the length of the gitea-test by creating a single
`makeGiteaTest` function which creates the configuration for a testcase
with a given database driver.
trace: warning: config.services.gitea.database.password will be stored as plaintext
in the Nix store. Use database.passwordFile instead.
(Arguably, this shouldn't be a warning at all. But making it happy is
easier than having a debate on the value of this warning.)
Although this can be added to `extraOptions` I figured that it makes
sense to add an option to explicitly promote this feature in our
documentation since most of the self-hosted gitea instances won't be
intended for common use I guess.
Also added a notice that this should be added after the initial deploy
as you have to register yourself using that feature unless the install
wizard is used.
