prometheus.exporter.kafka: fix for config option is ignored

[akhmatov-s]

PR Description

prometheus.exporter.kafka instance option is ignored in river.config.

Which issue(s) this PR fixes

I'm trying to start grafana-agent with a simple config, where kafka_uris has more than 1 node:

prometheus.exporter.kafka "LABEL" {
    kafka_uris = ["kafka1:9092", "kafka2:9092"]
    instance = "test-instance"
}

Getting error message:

Error: /etc/agent/config.river:1:1: Failed to build component: building component: an automatic value for `instance` cannot be determined from 2 kafka servers, manually provide one for this integration

1 |   prometheus.exporter.kafka "LABEL" {
  |  _^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
2 | |     kafka_uris = ["kafka1:9092", "kafka2:9092"]
3 | |     instance = "test-instance"
4 | | }
  | |_^
5 |

instance option is ignored.

The proposed PR fixes things for me.

[CLAassistant]

All committers have signed the CLA.

[tpaschalis]

Hey there @akhmatov-s, good catch!

Do you mind updating the docs for this new field as well?

[akhmatov-s]

Hey there @akhmatov-s, good catch!

Do you mind updating the docs for this new field as well?

The field is not new, it's already in the docs: the problem is the agent doesn't behave according to docs ignoring this option from config.

[erikbaranowski]

Thanks for the fix. Can you add a record in the CHANGELOG.md for this bug fix and fix up the tests/lint in CI?

[tpaschalis]

FYI @akhmatov-s I've created a CHANGELOG entry for you so we can move ahead with the PR.

Thank you for your contribution!