validate resource param exists

[aramase]

Reason for Change:

Validates if the resource parameter exists in the token request. This validation is currently done in the sdk and we are introducing the change in order to mimic the exact same error response code that IMDS would send for such a scenario.

Request without resource param while talking directly also returns an error and 400 response code -

body {"error":"invalid_request","error_description":"Required query variable 'resource' is missing"}
Response status: 400 Bad Request

With this change we will be more aligned with what a user would typically see while taking to IMDS without pod-identity.

Issue Fixed:

Notes for Reviewers:

[kkmsft]

/lgtm