docs: revert deprecation of metricName for Azure Monitor scaler

[lsolovey]

Revert the deprecation of metricName field in the Azure Monitor scaler (originally deprecated in #1074).

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• Commits are signed with Developer Certificate of Origin (DCO)

Fixes #1152

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[JorTurFer]

Nice!
Could you update the code as well to remove the deprecation message in case of this scaler?

[lsolovey]

Nice! Could you update the code as well to remove the deprecation message in case of this scaler?

@JorTurFer Yes, I will be sending a PR for that as well.

[lsolovey]

@JorTurFer I've just opened a separate PR for the code changes: kedacore/keda#4713