Support arbitrary git hosts

[furudean]

Add support to fetch plugins from arbitrary git hosts via git clone. It will use whatever the user's git config is to clone things.

These patterns are now possible:

fisher install https://git.sr.ht/~jlkde/note.fish
fisher install [email protected]:himawari.fun/bugstyle.fish
fisher install [email protected]:meaningful-ooo/[email protected]

We assume that any URL that doesn't match existing officially supported git hosts like github user/repo(@ref)? or (https?://)?gitlab.com/* is a git host.

I have tested this with these plugins:

jethrokuan/z
https://github.com/jorgebucaran/spark.fish.git
gitlab.com/mirdono/tucker
[email protected]:meaningful-ooo/[email protected]
[email protected]:himawari.fun/bugstyle.fish
https://git.sr.ht/~jlkde/note.fish

Fixes #801
Maybe fixes #745 as requests can be authenticated using ssh

[bdmorin]

I just took a stab at this, didn't see your PR, thank you!