feat(microservices): add Kafka heartbeat callback to KafkaContext

[kosh-b]

PR Checklist

Please check if your PR fulfills the following requirements:

• The commit message follows our guidelines: https://github.com/nestjs/nest/blob/master/CONTRIBUTING.md
• Tests for the changes have been added (for bug fixes / features)
• Docs have been added / updated (for bug fixes / features)

PR Type

Implements #9949

• Bugfix
• Feature
• Code style update (formatting, local variables)
• Refactoring (no functional changes, no api changes)
• Build related changes
• CI related changes
• Other... Please describe:

What is the current behavior?

#9949

Issue Number: 9949

What is the new behavior?

Adds heartbeat callback to KafkaContext (so it will be passed to the endpoint)

Does this PR introduce a breaking change?

• Yes
• No

Other information

[coveralls]

Pull Request Test Coverage Report for Build 302ab445-3d0a-4682-b9f8-8636af34c82e

• 1 of 1 (100.0%) changed or added relevant line in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.0009%) to 94.09%

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Totals
Change from base Build 9b0871a2-2869-48ee-9715-bc995a860ea4:	0.0009%
Covered Lines:	6050
Relevant Lines:	6430

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💛 - Coveralls

[kamilmysliwiec]

Thanks for your contribution!

Looks good to me. Would you like to create a PR to the docs (adding one little section showcasing the heartbeat fn usage)?

[kosh-b]

Thanks!

I've created a pr for the documentation of the KafkaContext.heartbeat:
nestjs/docs.nestjs.com#2409

I'm not native english speaker, so feel free to adjust if needed :)

Also, if you have any adjustments for this pr (in case I've missed something related to nestjs internals), please share :)

[kamilmysliwiec]

Thank you, @kosh-b! LGTM