More explicit error message for errro 429 QUOTA_EXCEEDED/TOO_MANY_REQUESTS

[gregory1g]

Problem description
https://github.com/camaraproject/Commonalities/blob/main/documentation/API-design-guidelines.md#61-standardized-use-of-camara-error-responses introduces two options for error 429 - QUOTA_EXCEEDED and TOO_MANY_REQUESTS:

429	QUOTA_EXCEEDED	Either out of resource quota or reaching rate limiting.
429	TOO_MANY_REQUESTS	Either out of resource quota or reaching rate limiting.

The problem is: for different error code identical error message is used. As a result, the human readable error message do not explicitly addresses the issue while the server "knows" if which of two mentioned reasons caused the error.

Expected behavior
Explicit error messages, for example:

429	QUOTA_EXCEEDED	Out of resource quota.
429	TOO_MANY_REQUESTS	Rate limits are reached.