Update cluster-ingress-operator to bootstrap router with required featuregates

The cluster-ingress-operator will propagate the relevant Tech-Preview feature gate down to the router. This feature gate will be added as a command-line argument called ROUTER_EXTERNAL_CERTIFICATE to the router and will not be user configurable.

Refer:

• https://github.com/openshift/api/pull/1387
• EP : https://github.com/openshift/enhancements/blob/master/enhancements/ingress/route-secret-injection-for-external-certificate-management.md

Acceptance criteria 

• Introduce new cmdline arg on router to inject ExternalCertificate fetauregate status
• Dev test if injected env is available in the router pod
• Update any affected UTs