`[name]_APPNAME` Support

[rektide]

Describe the feature

[name]_APPNAME is an environment variable that allows for using an application name other than the typical app name when looking in XDG-ish folders like ~/.config. There is, for example, nvim's NVIM_APPNAME, as an example implementation.

This is an important capability to let operators manage more than one instance of a thing. For instance with nvim, if you could create ~/.config/nvim-next-try then do NVIM_APPNAME=nvim-next-try nvim to try to use that config, while leaving your existing config intact & untouched. This is crucial to enabling the operator to work with multiple instances of a tool.

I would love to have [name]_APPNAME support built in to c12.

Additional information

• Would you be willing to help implement this feature?

[pi0]

PR welcome 🙏