Allow using different deno configs for different dirs

[kt3k]

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

I want to use 2 different deno configs in a single repository. They have different importMap settings which have conflicting entries.

Describe the solution you'd like

Auto-detect different deno.json in subdirectories, and partition their handling in the language server.

To override auto-detections, allow "deno.config" option to accept object value of the form:

{
  ...
  "deno.config": {
    "path/to/foo": "path/to/foo/deno.json",
    "path/to/bar": "path/to/bar/deno.json"
  }
  ...
}

and apply each config only to the corresponding directory.

[Leokuma]

Related #713

[mindreframer]

I see there is an open PR denoland/deno#20410 - Workspace support. Is this issue related to this PR?