feat(scaler): support cloudID and apiKey in elasticsearch scaler

[rcbop]

• Support providing cloudID and apiKey in Elasticsearch scaler enabling it to be used with ElasticSearch Service on Elastic Cloud.
• Add test case for missing apiKey parameters.
• Add test case for mutual exclusion between providing endpoint addresses and cloudID.
• Add test case for providing neither addresses nor cloudID.
• Fix TestElasticsearchGetMetricSpecForScaling, testCase[7] used as input returns a parsing error that was not being checked.

Checklist

• Commits are signed with Developer Certificate of Origin (DCO - learn more)
• Tests have been added
• A PR is opened to update the documentation on (repo) (if applicable) chore: add cloudID and apiKey to elasticsearch scaler keda-docs#966
• Changelog has been updated and is aligned with our changelog requirements

Relates to #3785

[JorTurFer]

Looking good, only small nit in changelog.
Could you open a PR too in docs, adding these new files?

[JorTurFer]

/run-e2e elastic*
Update: You can check the progress here

[rcbop]

Hi @JorTurFer, please review if the docs PR are according to project standards kedacore/keda-docs#966

[JorTurFer]

/run-e2e elastic*
Update: You can check the progress here

[JorTurFer]

LGTM!
Thanks for the contribution

[zroubalik]

Looking good, could you please resolve Tom's question on the docs PR? Then we can proceed with merging this. Thanks

[rcbop]

Hi, I've replied to the question. Sorry for the delay, I'm contributing outside business hours as a hobby. Let me know if you need improvements to the docs or new test cases, I'm a bit restricted on time but I'll try to respond ASAP.