Improve support for schema normalization

[dstrates]

What resources or data sources are affected?

resource_schemaregistry_schema

Feature Request

Currently all schema values are normalized via a custom type jsontypes.Normalized before being CRUD via the Schema Registry API (#27)

While this conforms to Schema Registry best practices it precludes those who are expecting to capture syntactic differences between schemas.

This issue is to add support for handling both normalized and non-normalized schemas in the provider.

References

confluentinc/terraform-provider-confluent#196