[prometheus-adapter] Add Support for sidecar containers

[rpriyanshu9]

Is your feature request related to a problem ?

Currently there is no support for having sidecar containers in the helm chart. If a service like AWS Managed Prometheus (AMP) is being used then the adapter needs support for authentication with AWS using sigv4. Creating this issue because #1568 is closed because of being stale.

Describe the solution you'd like.

It would be good if there was an option of defining sidecar containers within the helm chart. Something like a variable inside the values file, which can be referenced in the deployment template.

Describe alternatives you've considered.

To get past this issue right now, I've forked the helm chart and added the required changes in the fork.

Additional context.

No response

[rpriyanshu9]

Raised a PR for the same - #3737