ingress: add spec for ingress tests

[mayankshah1607]

This test would be responsible for testing if ingress controller pods injected with Linkerd are are able to correctly rewrite incoming headers to ensure that traffic is proxied correctly. The sample app to be used for this is emojivoto.
Based on the Linkerd docs, the following ingress controllers will be tested:

• Nginx
• Traefik
• GCE
• Ambassador
• Gloo
• Contour

All the required YAML files shall be provided along with the tests. The testing process can be broken down into the following assertions:

• Checking if the sample app is in a Running state
• Deploying each of the Ingress controllers and make sure they're in a Running state
• Ensure the services are reachable via Ingress
• Inject the Ingress controller's pods and wait for it to come to a Running state. Verify if the proxy container has been injected.
• Deploy the Ingress resource with the correct rules to rewrite headers to ensure Linkerd's service discovery is working
• Check if the services are reachable via the Ingress

[mayankshah1607]

Closed via #19