Certgen job should make sure cert is valid for the requested service

[jenshu]

Gloo Edge Version

1.12.x (beta)

Kubernetes Version

No response

Describe the bug

Prior to the gloo/gateway merge, the certgen job generated a cert for the gateway service. Now the service has been renamed to gloo. This causes errors on upgrades from older gloo releases.

Steps to reproduce the bug

Install a version of gloo from before the gloo/gateway merge:

helm repo update
helm install -n gloo-system gloo gloo/gloo --create-namespace --version v1.11.0

and then upgrade to a version post-gloo/gateway merge:

helm upgrade -n gloo-system gloo gloo/gloo --version v1.12.0-beta8 -f - <<EOF
gateway:
  validation:
    allowWarnings: false
    alwaysAcceptResources: false
    failurePolicy: Fail
EOF

It will fail with an error like this:

ExitError:  Error: UPGRADE FAILED: post-upgrade hooks failed: Internal error occurred: failed calling webhook
 "gloo.gloo-system.svc": Post "https://gloo.gloo-system.svc:443/validation?timeout=10s": x509: certificate is valid for 
gateway, gateway.gloo-system, gateway.gloo-system.svc, gateway.gloo-system.svc.cluster.local, not gloo.gloo-system.svc

Expected Behavior

When the certgen job checks to see if it can use an existing Secret, it should consider a cert with the old service name (gateway) as invalid, instead of trying to reuse it.

Additional Context

No response