[exporter/kafka]Decide the Kafka topic based on the value of the attribute.

[pyama86]

Description:
I've implemented the feature based on the discussion in the referenced issue. I'm assuming it will suffice in most cases if the text attributes are available, so I haven't planned for arrays or maps.

Link to tracking Issue:
Fixes #31178

Testing:
I've implemented unit tests. For the tests related to kafka_exporter, I followed the existing implementation, but I find it somewhat redundant. If it's okay, I'd like to switch to table-driven tests.

Documentation:

After the discussion in the PR, I believe the final implementation will be determined, so I'll add documentation once we have a clearer idea of the direction.

[pyama86]

@crobert-1
Thank you for your polite review. I have reflected on the points you made. I wanted to make the implementation of obtaining the first value of an attribute a bit more DRY, but since I couldn't find a suitable existing interface, I've temporarily addressed it with an anonymous function. If it's okay to create an interface, I will do so.

[crobert-1]

LGTM, thanks for your making all of the updates, and for your contribution here @pyama86!

[pyama86]

@crobert-1
Thank you very much. I am also grateful for your dedicated review. Looking back, I feel I was too reserved about this repository, so I would like to proceed without hesitation, such as adding interfaces right from the start, next time.

[github-actions]

This PR was marked stale due to lack of activity. It will be closed in 14 days.

[TylerHelmuth]

@pyama86 looks like the linter is upset

kafkaexporter/kafka_exporter_test.go:376: File is not `gofmt`-ed with `-s` `-r 'interface{} -> any'` (gofmt)
		resource  interface{}
Error: kafkaexporter/kafka_exporter_test.go:430:22: G601: Implicit memory aliasing in for loop. (gosec)
				topic = getTopic(&tt.cfg, r)
				                 ^
Error: kafkaexporter/kafka_exporter_test.go:432:22: G601: Implicit memory aliasing in for loop. (gosec)
				topic = getTopic(&tt.cfg, r)
				                 ^
Error: kafkaexporter/kafka_exporter_test.go:434:22: G601: Implicit memory aliasing in for loop. (gosec)
				topic = getTopic(&tt.cfg, r)

[pyama86]

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