Allow passing argument to jsonnet binary

Hi,

i'm using jrsonnet binary as jsonnet binary replacement and use an experimental feature there, for that reason i need to pass an extra argument to the binary. It would be nice to allow setting this via the language server to use inside of vs code rather than command line

No files, tests, or entry points are identified in the issue. Start by tracing how the language server configures and invokes the Jsonnet executable for VS Code, then locate the configuration path for executable arguments. Done means an extra argument can be configured and reaches the binary invocation, with coverage in an appropriate test.

Written by the indexing model from the issue text.