fix: Prevented memory leak generated by not correctly cleaned HTTP resources

[JorTurFer]

After profiling KEDA operator looking for this memory leak, I found a weird behavior.
When I deploy the OP given SO, during the first minutes, prometheus trigger returns 404 and the memory grows, but at some point, the memory usage becomes stable and then prometheus trigger start to produce timeouts.

This impacts in 2 way, significativelly increasing the allocation of HTTP resources

And also increasing the size of the in use memory due to stored rootCAs of the clients (we are cloning the current cached certs but we aren't modifying the cloned item, so doesn't make sense, at least atm)

In order to solve these issues, this PR does:

• enforcing the Idle Connection closing during (scaler).Close(context.Context) to close them deterministically and not delegating this action to the garbage collector. This helps to reduce the allocated resources for stablishing connections
• returning the rootCAs item directly instead of cloning it, as we don't need to modify it (at least for the moment) so doesn't make sense creating a copy every time when it's requested. This helps to reduce in use memory for storing the copies (one per HTTP Client can generate several instances until de GC collects them if the scaler fails all the time and KEDA regenerates the scaler cache all the time). If we need to modify it in the future, we should think about how to improve this

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Fixes #5248

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[JorTurFer]

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

[JorTurFer]

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

[zroubalik]

LGTM, great job!

[rameshbabu009]

"scaler": "prometheusScaler", "error": "prometheus query api returned error. status: 403 response: {"message":"Credential should be scoped to a valid region. "}"} any suggestions on this error

[JorTurFer]

"scaler": "prometheusScaler", "error": "prometheus query api returned error. status: 403 response: {"message":"Credential should be scoped to a valid region. "}"} any suggestions on this error

This issue was closed 4 months ago and it's totally unrelated with your topic. I'd suggest opening a new issue for your case