[UI] gloo-fed console breaks when rendering RTs that contain header matchers

[lgadban]

Describe the bug gloo-fed console breaks when rendering RTs that contain header matchers

To Reproduce

1. Apply VS and RT

   
   apiVersion: gateway.solo.io/v1
   kind: VirtualService
   metadata:
   name: petstore
   namespace: gloo-system
   spec:
   virtualHost:
   domains:
   - '*'
   routes:
   - delegateAction:
       selector:
         labels:
           routes: petstore
         namespaces:
         - gloo-system
     matchers:
     - prefix: /
   ---
   apiVersion: gateway.solo.io/v1
   kind: RouteTable
   metadata:
   labels:
   routes: petstore
   name: petstore-routes
   namespace: gloo-system
   spec:
   routes:
   - matchers:
   - headers:
     - name: foo
       regex: true
       value: .*bar.*
     methods:
     - GET
     prefix: /
   routeAction:
     single:
       upstream:
         name: default-petstore-8080
         namespace: gloo-system

3. See error
<img width="783" alt="Screen Shot 2021-10-27 at 3 18 59 PM" src="https://user-images.githubusercontent.com/1161279/139141398-4fa21552-68f8-4867-b515-feb25013746c.png">

**Expected behavior**
RT shown with no errors

**Additional context**
GlooE 1.8.15

[chrisgaun]

We need to backport this to 1.8

[github-actions[bot]]

This issue has been marked as stale because of no activity in the last 180 days. It will be closed in the next 180 days unless it is tagged "no stalebot" or other activity occurs.