[LSP] Support import path includes in the lsp

[acx-yz]

Is your feature request related to a problem? Please describe.
discussion

Describe the solution you'd like
Similar to the -I flag on nickel export you should be able to set a path for relative lookups on imports.

Describe alternatives you've considered
As a workaround, I'm using relative file paths everywhere to avoid LSP errors everywhere for valid files.