Added schema id check to the JsonSchemaResolver

[gokerakc]

Issue: $id property is not required for JSON schemas but in the JsonSchemaResolver class we need to use the schema id value and there is no null check in place for it.

Current behavior: JsonSchemaResolver throws the following error when the provided schema does not have a schema id;

• System.ArgumentNullException: 'Value cannot be null. Arg_ParamName_Name' (error reason is not clear)

Desired behavior: JsonSchemaResolver throws the following exception when the schema id is null;

• System.Exception: 'Provided schema does not have $id property.'

If you have a different solution for this issue or any suggestion for the exception message please let me know.

[cla-assistant[bot]]

All committers have signed the CLA.

[rayokota]

Null checked added here https://github.com/confluentinc/confluent-kafka-dotnet/pull/2226