Feat: Add ErrorMessage class for Schema Registry client.

[an2x]

Adding a modified version of io.confluent.kafka.schemaregistry.client.rest.entities.ErrorMessage from the Confluent Schema Registry Client, which has the same structure in Java and is still fully compatible with the client code, but supports parsing the source JSON error message in more formats via Jackson annotations.

Pre-pending this auth library to the classpath of an application using a Schema Registry client will override the class implementation and will allow parsing Managed Kafka style error messages.

If using Maven, this can be achieved by adding this dependency first in the pom.xml file:

<dependencies>
    <dependency>
      <groupId>com.google.cloud.hosted.kafka</groupId>
      <artifactId>managed-kafka-auth-login-handler</artifactId>
      <version>1.0.6</version>
    </dependency>
    ... other dependencies ...
</dependencies>

If running an existing application from the command line, the jar file needs to be pre-pended to the classpath:

java -cp managed-kafka-auth-login-handler-1.0.6.jar:<other class path entries> <main class>