Allow using a relative path or find the executable on PATH

[SuperSandro2000]

I am sharing my vscode config with multiple machines which have different users. I have shfmt installed in my home directory and would like to use ~, $HOME or just depend on $PATH to find the shfmt binary.

[bboysnick5]

Also wanted. I have multiple OSes. In the meantime just don't sync this setting in VS if you do.

[j-lakeman]

Would also much appreciate that!
Maybe looking into this helps, as they also have a similar executable setting, which evaluates the given string for the user's environment:

https://github.com/vscode-shellcheck/vscode-shellcheck/blob/bdc826c830abb671d35f497e81147c3480ddca8a/src/settings.ts#L112C5-L112C5