feat: Add broker communication mode

[dominikriemer]

Purpose

This PR introduces the initial broker-based communication mode for core-to-extension requests using NATS request/reply, as a foundation to remove the need for an open incoming HTTP port on extension services.

• Added transport-mode configuration (http, nats, auto/dual) via environment support in commons.
• Added shared broker transport model in streampipes-model
• Added new module streampipes-nats-extensions for extension-side broker request handling.
• Added core-side NATS request/reply client and transport-aware request manager wiring in streampipes-service-core.
• Extended ExtensionServiceRequestTarget/ExtensionServiceRequestTargets to carry operation-aware routing (HTTP path + broker topic semantics).
• Integrated broker receiver startup/shutdown into extension service bootstrap (streampipes-service-extensions).
• Implemented NATS handlers for SERVICE_LOAD, ADAPTER_STATE_CHANGE (start/stop)
• Added support in core manager to send requestAdapterStateChange via NATS (including auth token in envelope).
• Kept HTTP flow intact for backward compatibility and migration safety.

Behavior

Core transport selection is now mode-based:
http: always HTTP
nats: always NATS
auto: prefer NATS for services advertising broker support, otherwise HTTP
Extension runtime can be configured to run HTTP-only, NATS-only, or dual mode.

Remarks

PR introduces (a) breaking change(s): no

PR introduces (a) deprecation(s): no