[receiver/kafkareceiver] Add otlp_json support in kafka receiver

[joeyyy09]

Description:

The current features dont support otlp_json in receivers/kafkareceivers.

Add support for otlp_json which accepts json formated for Otel Collector kafka receiver
Link to tracking Issue: #33627

Testing:
Added test files for the same.

Documentation:

[joeyyy09]

this is a draft in process, would love to see if im going in the right direction or not.

[yurishkuro]

@joeyyy09 check the linter failures
kafkareceiver/unmarshaler.go:61: File is not gci-ed with --skip-generated -s standard -s default -s prefix(github.com/open-telemetry/opentelemetry-collector-contrib) (gci)

[joeyyy09]

@joeyyy09 check the linter failures kafkareceiver/unmarshaler.go:61: File is not gci-ed with --skip-generated -s standard -s default -s prefix(github.com/open-telemetry/opentelemetry-collector-contrib) (gci)

My bad, fixed that.

[thmshmm]

Support for encoding extensions in the kafkareceiver was just merged with #33888. Using the otlpencodingextension should now do the job.

[yurishkuro]

Prom tests are failing on main, not an issue here (#35119). Everything else in the PR is green. @open-telemetry/collector-maintainers this can be merged.

@thmshmm I think an upgrade to otlpencodingextension is an independent issue and can be tackled separately, there's no need for it to block this PR.