KIP-1273 — Improve Connect configurable components discoverability

Accepted Kafka 4.3 Connect

Introduces a shared Configurable interface with a config() method across all Kafka Connect pluggable component types (Connector, Converter, Transformation, Predicate), and adds a REST endpoint to expose component configuration metadata. Each component type currently defines config() independently with no common supertype, making it impossible to generically discover and document configuration for all plugin types.

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