Better error handling when retrieving Avro schemas from registry

[abhishekrb19]

Currently, when retrieving an Avro schema from the registry and if the request fails with an IOException or a RestClientException, we bubble this generic error up to the user:

"Failed to fetch Avro schema id[233323] from registry. Check if the schema exists in the registry. Otherwise it
could mean that there is malformed data in the stream or data that doesn't conform to the schema"
specified."

However, this error message is misleading in cases where the server is throwing unauthorized/forbidden error codes via RestClientException. So now we handle IOException and RestClientException separately so that we can bubble up more specific errors rather than the common template.

Added unit tests for the change and also cleaned up test annotations @Test(expected = ParseException.class) by adding better tests assertions.

This PR has:

• been self-reviewed.
• added unit tests or modified existing tests to cover new code paths, ensuring the threshold for code coverage is met.

[amaechler]

🐻 Thanks!

[zachjsh]

😎