Added alternative expression field in AWS CloudWatch scaler

[dekelev]

Signed-off-by: Dekel Barzilay dekelev@gmail.com

Relates to changes from these PRs kedacore/keda#2911 & kedacore/keda#2997

Added alternative expression field in AWS CloudWatch scaler.
Here's an example ScaledObject config:

awsRegion: us-east-1
expression: >-
  SELECT MIN(MessageCount) FROM "AWS/AmazonMQ" WHERE Broker =
  'production' and Queue = 'worker'
metricCollectionTime: '60'
metricName: WorkerMessageCount
metricStatPeriod: '60'
minMetricValue: '0'
namespace: AWS/AmazonMQ
targetMetricValue: '100'

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[JorTurFer]

Please, instead of explaining those fields there, mark them as optional and describe them in the section Parameter lists:(below).
I mean, take the descriptions from these 3 fields and add them below (I know that they are already wrong), we follow this convention for having a unified documentation (but sometimes this could happen)

[dekelev]

Please, instead of explaining those fields there, mark them as optional and describe them in the section Parameter lists:(below). I mean, take the descriptions from these 3 fields and add them below (I know that they are already wrong), we follow this convention for having a unified documentation (but sometimes this could happen)

Done

[JorTurFer]

LGTM!

[zroubalik]

LGTM