Option to use message count as metric in kafka scaler on invalid offset

[DaniilAnichin]

Provide a description of what has been changed

Checklist

• [*] When introducing a new scaler, I agree with the scaling governance policy
• [*] I have verified that my change is according to the deprecations & breaking changes policy
• [*] Tests have been added
• [*] Changelog has been updated and is aligned with our changelog requirements
• [*] A PR is opened to update our Helm chart (repo) (if applicable, ie. when deployment manifests are modified) - I did my best to check, but it looks like no changes required
• [*] A PR is opened to update the documentation on (repo) (if applicable)
• [*] Commits are signed with Developer Certificate of Origin (DCO - learn more)

Fixes #

Relates to keda-docs PR

[DaniilAnichin]

Hi, I did my best to prepare the PR in the appropriate way (signed commits, added tests, added docs PR)
I'm not very good with go though, and I'm pretty sure my code changes itself are suboptimal.
I think it would be best to adjust the calls in such a way that earliest offsets are only loaded when the flag is set, but I did not get how exactly to do so, since it's done on the outside and passed as parameter, so we would need to type it as (some data or null) or something that direction.
I would love if someone close to the kafka scalers / project in general would advise on should I optimize it or it's good enough as is

Also I didn't touch experimental kafka-go scaler, to minimize back-n-force (assumed it would be better to polish one first, than copy to the second one if required)

P.S.: For what it's worth, I did build this version locally and deployed to the cluster, and it seems to work as expected so far

[DaniilAnichin]

Based on other PRs, I'll tag @JorTurFer , @zroubalik and @dttung2905
Excuse me if this is exessive

[JorTurFer]

The code looks correct, but I don't know anything about kafka, @dttung2905 or @zroubalik PTAL

[dttung2905]

So sorry for the late reply. I have put a 👀 icon on it and was actually reviewing the PR. But for some reason I left half way and totally forget about it 😞
LGTM too !

[DaniilAnichin]

/run-e2e kafka

[dttung2905]

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