[FEATURE] - Add Auth to RedpandaSchemaRegistry

[awmatheson]

Is your feature request related to a problem? Please describe.
There is currently no mechanism for authenticating with the Redpanda schema registry.

So if you are trying to reach the registry you will receive an error like:

Exception has occurred: HTTPError
401 Client Error: Unauthorized for url: https://schema-registry-xxxxd08.cxxxxx.byoc.prd.cloud.redpanda.com:30081/subjects/%7B%0A%20%20%20%20%22type%22:%20%22record%22,%0A%20%20%20%20%22name%22 <rest of error removed as it's message contents> 

Describe the solution you'd like
It seems like it accepts basic auth, so there should be a way to specify a username and password and pass that with the requests module.

[Psykopear]

I opened #398 adding a headers option to the schema registry, that can be forwarded to all the requests there and be used for authentication