ResolveCanvas API

[begelundmuller]

This PR introduces a new API ResolveCanvas. It is a single convenience API, which is equivalent to separately:

1. Calling GetResource to get the canvas
2. Then calling ResolveComponent for each of the canvas's components
3. Then calling GetResource to lookup the metrics view(s) referenced by each of the components

The type signature for the API is:

// ResolveCanvas is a convenience API that returns a canvas and all its referenced components and metrics views.
rpc ResolveCanvas(ResolveCanvasRequest) returns (ResolveCanvasResponse) {
  option (google.api.http) = {
    post: "/v1/instances/{instance_id}/queries/canvases/{canvas}/resolve",
    body: "*"
  };
}

message ResolveCanvasRequest {
  // Instance ID
  string instance_id = 1;
  // Canvas name
  string canvas = 2;
  // Optional args for resolving templating in the component properties
  google.protobuf.Struct args = 3;
}

message ResolveCanvasResponse {
  // The canvas resource.
  Resource canvas = 1;
  // All the component resources referenced by the canvas.
  // The resources state.valid_spec.renderer_properties will have templating resolved for the provided args.
  // (Corresponds to calling the ResolveComponent API for each component referenced in the canvas spec).
  map<string, Resource> resolved_components = 2;
  // All the metrics view resources referenced in the components' renderer_properties.metrics_view field.
  map<string, Resource> referenced_metrics_views = 3;
}

Closes #6364