Add support for full url references for client operations get/patch/delete

[ruscoder]

client.get('https://example.com/fhir/Patient/123')

and

client.get('Patient/123')

should work identically if base URL matches

[ruscoder]

I'm not sure that base-url validation will be useful in typical use cases as part of any sdks (e.g. aidbox-python-sdk), because internally fhir client might use internal base URL (e.g. http://devbox:8080), while the public URL is different (e.g. https://example.com)