[Feature Request] Allow HTTP gist init to make repository with different visibility

[Juliaria08]

Use the git feature for server-specific push-options, and make one called visibility allowing public, unlisted, and private as values.

Edit: Noticed there's git-push-options, but that's not usable unless we want to manually send an empty commit at first, and then it'd only work if we wanted to make it private, because a crawler could otherwise get the gist's URL. (yes you could generate a new UUID but then the process of creating a hidden gist is less useful)

Edit2: I reloaded the web app, and saw that the gists I tried to create with git push -o visibility=unlisted -u origin master, and git push returned:

fatal: the receiving end does not support push options
fatal: the remote end hung up unexpectedly
error: failed to push some refs to 'https://gist.tilde.green/init'

Also made them have no revisions, making it having to manually push a revision for it to be able to be deleted. (Note, I didn't push a revision but I deleted the 0 revision gists from the admin dashboard)

Edit3: More info about the instance:

Opengist 	v1.7.3
Go 	go1.22.6
Git 	2.46.0