Improve AWS Cloudwatch Scaler metric exporting logic

[fivesheep]

Signed-off-by: Xiayang Wu xwu@rippling.com

Provide a description of what has been changed
To address the issues mentioned in #2242

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 aws cloudwatch scaler doc keda-docs#568
• Changelog has been updated

Fixes #

• Truncate/Round down the endtime based on the metrics period setting to provide better performance and avoid getting empty data
• startTime to be based on the endTime(to avoid two time.now() calls)
• Add a new param named metricEndTimeOffset to allow skipping the most recent data point from cloudwatch
• Add a new param named metricUnit to allow passing a metric Unit which is needed by some metrics

[zroubalik]

Generally seems to be ok, could you please add unit tests for the new functionality and modify documentation on kedacore/keda-docs? Thanks

[JorTurFer]

LGTM! Thanks a ton for the changes :)

[zroubalik]

Could you please update docs and fix the linter problems? https://github.com/kedacore/keda/runs/4089628384?check_suite_focus=true

[zroubalik]

@fivesheep fyi you can run the static check locally if you configur precommit or you can run make golangci. This should help you tackling the linter problems.

[fivesheep]

@JorTurFer a couple more changes were made to fix the linting issue. need to introduce two helper function to reduce the number of if-elses, please review again. thx!

[JorTurFer]

LGTM!
Let's wait until the validations are finished to check that all is good.
BTW, thanks a ton for your effort updating this AWS scaler! ❤️ ❤️

[JorTurFer]

One more thing, could you update the CHANGELOG please?
I have just seen that you didn't update it

[fivesheep]

There's a timeout on the failed check, not sure how to re-trigger it

[JorTurFer]

Thanks! :)
Maybe @zroubalik could re-execute it. Let's wait until he has time

[zroubalik]

Once comments on doc PR are resolved we can merge this :)

[zroubalik]

Thanks a lot for the contribution!