feat: `sar_download_file <url> <filepath> [directory]`

[ThisAMJ]

This could potentially be unsafe, but it could also automate srconfigs updates, challenge_maplist, fast taunts, containerridesave, vault save, tram save, etc. Just be careful with usage, it overwrites!

Smartly looks through game directories for existing file to overwrite (even p2common), falls back to main game directory i.e. portal2 / portalreloaded / whatever if file doesn't exist.

[mlugg]

I'm going to give this a bit more thought before merging, so don't think I'm ignoring it

[NeKzor]

Blocked by https://github.com/p2sr/SourceAutoRecord/issues/187