[Schema Registry] Add convenience layer for SchemaRegistryClient

[ramya-rao-a]

This issue is a follow up for #10076

Using the Java SchemaRegistryClient as a reference, add a convenience layer to the generated client in @azure/schema-registry package applying TypeScript SDK guidelines.

The corresponding package in Java has interfaces for Codec and Serializer. As part of this issue, we will be not be focusing on these and only be adding a layer over the auto generated code.

[ramya-rao-a]

Ignore caching as part of this task, we can explore that in #10438

[nguerrera]

Ha, I was just typing a comment that we should probably exclude caching in the first pass, given the uncertainty in the Java review about which layer should handle this and so on. :)

[nguerrera]

#10602 is out for review that implements the convenience layer + unit tests. Samples and setting package to publish to follow after that.

[nguerrera]

This is now done. Samples and setting packages to publish included in #10890