Implement retry logic on downloader

[Shunpoco]

Describe your changes

A downloader needs a retry logic for curl, because sometimes network trouble happens.

This PR does:

• Add a retry logic in the downloader shell script. The number of retry and sleep duration between iteration are configurable
• Modify helm chart to add a ConfigMap for setting those variables on downloader container
• Modify Reconciler code to add the ConfigMap if it is specified
• Add a verification step for a ConfigMap from helm chart to actual installer pod

Issue ticket number and link

#591

Checklist before requesting a review

• I have performed a self-review of my code
• If it is a core feature, I have added thorough tests.
• I tested the changes with the following distributions:
  • Kind
  • MiniKube
  • MicroK8s
  • Rancher RKE2
  • Azure AKS
  • GCP GKE (Ubuntu nodes)
  • AWS EKS (AmazonLinux2 nodes)
  • AWS EKS (Ubuntu nodes)
  • Digital Ocean Kubernetes