Create schemaGroup API to register group names

[harshach]

This is intended to create a admin page on the UI side to register schema group names , instead free-form text like today. Once we do this we can enable rules on schema names , example Kafka group requires suffixing ":v" or ":k" with the schema names. We've lot of users trip over this registration naming scheme. Also having a predefined schemaGroup name allows users not to make mistakes in registering the schema.