ccompat: support mode per subject

[yvespp]

Feature or Problem Description

Currently ccompat doesn't support POST/DELETE/GET of mode per subject. Confluent schema registry API: https://docs.confluent.io/platform/current/schema-registry/develop/api.html#get--mode-(string-%20subject) Mode is only supported for the whole registry.

Proposed Solution

Implement POST/DELETE/GET per subject for ccompat.

Additional Context

I use Apicurio together with Quarkus in dev/test mode. It would be nice if I could run tests locally against Apicurio and don't need to set up my own confluent schema registry.

[apicurio-bot[bot]]

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Pinging @EricWittmann to respond or triage.