FR: Custom Foundry installation location

[beepidibop]

My forge build is a bit messed up, the extension isn't picking up where my forge is even though where forge is working.

I see this was an issue here #354 but I didn't install with cargo, so my default installation location didn't line up with #366 or #515.

Submitting this feature request since the template for the PR asks me to discuss it in issues before submitting a PR. I have a branch ready for the PR if this is approved.

[oxcabe]

I am also interested in this config feature, since Flatpak sandboxing is messing with the forge binary lookup:

Foundry project 'foundry-project' was not able to initialize correctly:
Error: Couldn't find forge binary. Performed lookup:
["forge","/home/oxcabe/.var/app/com.vscodium.codium/config/.foundry/bin/forge"]

If I were to request extra (or either implement it myself) for this feature, I'd ask for an additional "args" array config field to pass arguments to the forge binary. That way, it is not necessary to alter sandboxing permissions by calling /usr/bin/flatpak-spawn with forge as the positional argument.