feat: add Kafka invocation support to func invoke

[singhshresth26]

Changes

• 🎁 Add support for invoking Kafka functions by producing a test message directly to the configured topic.
• 🧹 Bypass local/remote HTTP route lookup when the invocation format is kafka.
• 🧹 Add kafka as a valid option to the Invoke field jsonschema tags and regenerate the func.yaml configuration schema.
• 🧹 Introduce a mocked kafkaWriter interface to write clean unit tests for Kafka message production without requiring a live broker.

/kind enhancement

Fixes #3931

Release Note

Added support to the CLI for invoking Kafka functions. When a function has `invoke: kafka` configured, the `func invoke` command will read `KAFKA_BROKERS` and `KAFKA_TOPICS` from `func.yaml` (interpolated) and produce a test message directly to the configured topic(s).

[linux-foundation-easycla]

The committers listed above are authorized under a signed CLA.

• ✅ login: singhshresth26 / name: Shresth Singh (c1d1608)

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[knative-prow]

Welcome @singhshresth26! It looks like this is your first PR to knative/func 🎉

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