feat: Add support custom metricName in RabbitMQ scaler

[rtnpro]

This change adds support for parsing custom metricName in RabbitMQ scaler, and help to workaround use cases where there's reconcile error for a ScaledObject having duplicate auto generated metricNames, e.g., multiple trigger on the same queue, mode but from different RabbitMQ hosts.

Checklist

• Commits are signed with Developer Certificate of Origin (DCO - learn more)
• Tests have been added
• [ ] A PR is opened to update our Helm chart (repo) (if applicable, ie. when deployment manifests are modified)
• A PR is opened to update the documentation on (Update RabbitMQ scaler docs for adding custom metric name support keda-docs#499) (if applicable)
• Changelog has been updated

Fixes #1975

[rtnpro]

I need some suggestions on how to fix the tests here: https://github.com/kedacore/keda/blob/main/pkg/scalers/rabbitmq_scaler_test.go#L94-L104. I see that there's no assertion on the generated Metadata, but checks to just assert if parsing trigger metadata was successful.

Should I add a new function and some test data to assert if we are parsing custom metricName properly?

[zroubalik]

I need some suggestions on how to fix the tests here: https://github.com/kedacore/keda/blob/main/pkg/scalers/rabbitmq_scaler_test.go#L94-L104. I see that there's no assertion on the generated Metadata, but checks to just assert if parsing trigger metadata was successful.

Should I add a new function and some test data to assert if we are parsing custom metricName properly?

Yeah, that would be nice!

[zroubalik]

@rtnpro would you mind fixing the conflicts, failures and linter problems? Thanks!

[rtnpro]

@zroubalik I have updated the test data rabbitMQMetricIdentifiers to assert if custom metric names are used to generate metric names correctly. RabbitMQ scaler tests run successfully.

Let me know what you think about: 2e15f18

[zroubalik]

Looking good, could you please update Changelog and update documentation on kedacore/keda-docs ? Thanks

[zroubalik]

LGTM, thanks a lot for the contribution!

[rtnpro]

@zroubalik I have added the docs fix here: kedacore/keda-docs#499. Thanks for reviewing the PR :)