Allow configuring path to language server

[Gert-dev]

Thanks for this package!

It would be neat if there was a setting in this package that allowed configuring the path to the language server instead of requiring to put it in a directory that is part of the PATH environment variable. This would allow building and installing the language server somewhere non-globally.

[mads-hartmann]

@Gert-dev Sure thing, I'll sit together with @skovhus this weekend to work on a few features. Hopefully we'll have time to look at this as well :)