getSubmissionStatus returns incorrect error response on unsupported transaction type

[Aleš Bizjak]

Bug Description

The submissionStatus endpoint only supports transfers and account creations, this is documented and deliberate.
However if querying submission status of an unsupported transaction the response is

{"error":0,"errorMessage":"Cannot communicate with node via GRPC endpoint"}

which is incorrect. The error should be more precise and not misleading.

Steps to Reproduce

Query submissionStatus for an unsupported transaction type.

Expected Result

Get an error result indicating that the type is unsupported, and "InvalidRequest" status code.

Actual Result

Misleading error result and status code 502.