feat: Allow setting ARGOCD_EXEC_TIMEOUT in repo server

[jannfis]

What type of PR is this?

/kind enhancement

What does this PR do / why we need it:

There's currently no way to set the environment variable for ARGOCD_EXEC_TIMEOUT in the repository server. This PR introduces this setting as first class feature by introducing .spec.repo.execTimeout, which if set, will add the appropriate environment variable to the repo server's pod template.

Have you updated the necessary documentation?

• Documentation update is required by this PR.
• Documentation has been updated

how are the referenced docs actually updated? can't find refdocs anywhere 😁

Which issue(s) this PR fixes:

Fixes #?

How to test changes / Special notes to the reviewer:

• Create ArgoCD CR:

apiVersion: argoproj.io/v1alpha1
kind: ArgoCD
metadata:
   name: argocd
spec:
  route:
    enabled: true
  repo:
    execTimeout: 600

• Apply to cluster in some-ns
• Get environment variables from repo server pod: kubectl get deployment argocd-repo-server -o jsonpath='{.spec.template.spec.containers[0].env}'
• It should contain ARGOCD_EXEC_TIMEOUT with value of 600
• Set .spec.repo.execTimeout to value 300
• Get environment variables from repo server pod: kubectl get deployment argocd-repo-server -o jsonpath='{.spec.template.spec.containers[0].env}'
• It should contain ARGOCD_EXEC_TIMEOUT with value of 300
• Remove .spec.repo.execTimeout from ArgoCD CR in cluster
• Wait for reconciliation
• Get environment variables from repo server pod: kubectl get deployment argocd-repo-server -o jsonpath='{.spec.template.spec.containers[0].env}'
• It should not contain any ARGOCD_EXEC_TIMEOUT variable anymore

[iam-veeramalla]

LGTM !! Thanks @jannfis for the quick PR

[iam-veeramalla]

👍