fix fallback envoy version check bug

[PerforMance308]

Ⅰ. Describe what this PR did

Our Evnoy version is 1.20, while the fallback feature requires Envoy version at lease 1.20.6.

The initial version higress-data-plane support fallback, we can remove this version check directly.

Ⅱ. Does this pull request fix one issue?

fixes #431

Ⅲ. Why don't you add test cases (unit test/integration test)?

I added test file to test/e2e/conformance/tests

Ⅳ. Describe how to verify it

run make higress-conformance-test

Ⅴ. Special notes for reviews

[codecov-commenter]

Codecov Report

Merging #441 (0ed69ec) into main (124caf8) will increase coverage by 0.24%.
The diff coverage is n/a.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #441      +/-   ##
==========================================
+ Coverage   37.24%   37.49%   +0.24%     
==========================================
  Files          65       65              
  Lines        9215     9215              
==========================================
+ Hits         3432     3455      +23     
+ Misses       5517     5495      -22     
+ Partials      266      265       -1     

see 1 file with indirect coverage changes

[johnlanni]

This annotation value should be a service name in the same namespace, see: https://kubernetes.github.io/ingress-nginx/user-guide/nginx-configuration/annotations/#default-backend

[johnlanni]

This e2e test case doesn't seem to make sense, you should check that request is routed to the default backend service when the ingress's service doesn't exist.

[SpecialYang]

You can also check the fallback via the normal ingress and the corresponding canary ingress.

For example,

apiVersion: networking.k8s.io/v1
kind: Ingress
metadata:
  name: normal
  namespace: default
spec:
  ingressClassName: higress
  rules:
    - host: test.com
      http:
        paths:
          - backend:
              service:
                name: demo
                port:
                  number: 8080
            path: /header
            pathType: ImplementationSpecific
---
apiVersion: networking.k8s.io/v1
kind: Ingress
metadata:
  annotations:
    nginx.ingress.kubernetes.io/canary: 'true'
    nginx.ingress.kubernetes.io/canary-by-header: x-user-id
    nginx.ingress.kubernetes.io/canary-by-header-value: "100"
  name:  canary
  namespace: default
spec:
  ingressClassName: higres
  rules:
    - host: test.com
      http:
        paths:
          - backend:
              service:
                name: demo-canary
                port:
                  number: 8080
            path: /header
            pathType: ImplementationSpecific

If the service demo-canry doesn't exist, the following request will fallback to demo.

curl -H "host: test.com" -H "x-user-id: 100"  x.x.x.x/header