Add support for a custom Kafka topic prefix in Hono components

[yasemindogan93]

Issue Description

We would like to introduce a configuration property for Hono-based components to prepend a custom prefix to Kafka topic names. Currently, Hono topics follow a fixed naming scheme (e.g. hono.event.<tenant>). In some environments (e.g. multi-tenant or multi-cluster deployments), it is desirable to have an additional prefix (such as myPrefix.hono.event.<tenant>).

We propose adding a configuration option (e.g. hono.kafka.topicPrefix) that can be set via Quarkus or environment variables. All components should then consistently apply this prefix when creating or subscribing to Kafka topics.

Key Points

1. Add a new config property (e.g. hono.kafka.topicPrefix).
2. Apply this property across components (adapter, command router, auth service, registry, etc.) so that all Kafka producers/consumers use the custom prefix.
3. Maintain backwards compatibility: if no prefix is set, the existing naming (e.g. hono.telemetry.<tenant>) should remain.

Rationale

Allows running multiple Hono-based environments in the same Kafka cluster.
Simplifies isolation or naming consistency across teams or tenants.

[sophokles73]

Can't you do the same by simply using a prefix in the tenant ID for grouping tenants?

[yasemindogan93]

You can certainly prefix the tenant ID, but that effectively bakes “environment” or “deployment” details right into the tenant name. In many cases, the tenant ID is managed externally or needs to remain “clean” (e.g. it is referenced in device registries, authorization rules, IoT management tools, etc.). A dedicated configuration property for a global prefix keeps the environment-specific or cluster-specific detail separate from tenant identities and ensures that Hono’s components can uniformly apply the prefix without forcing every tenant ID to include it.

[sophokles73]

Ok, I see your point. Are you going to create a corresponding PR?

[yasemindogan93]

Thanks for following up! I've already created a fork and am currently working on a PR. Once I finish making the necessary changes and verifying everything works as expected, I'll open the PR.