api: fix WasmCodeSourceType enum validation

[eguzki]

What

This PR fixes the validation enum values of the WasmCodeSourceType type.

When the following EnvoyExtensionPolicy resource was deployed, the CRD validation failed

---
apiVersion: gateway.envoyproxy.io/v1alpha1
kind: EnvoyExtensionPolicy
metadata:
  name: my-wasm-1
  namespace: envoy-gateway-system
spec:
  targetRef:
    kind: Gateway
    name: eg
    group: gateway.networking.k8s.io
  wasm:
    - name: my_wasm_1
      code:
        type: Image
        image:
          url: oci://example.com/project/my-wasm:latest
          pullSecret:
            name: "some-secret-name"
      failOpen: true
      config:
        foo: value1

The validation message:

The EnvoyExtensionPolicy "my-wasm-1" is invalid: 
* spec.wasm[0].code.type: Unsupported value: "Image": supported values: "Global", "Local"
* <nil>: Invalid value: "": "spec.wasm[0].code.type" must validate all the schemas (allOf)

Verification steps

• Checkout the current branch
• Create local Kind cluster

make create-cluster

• Build custom image

make kube-install-image

• Run custom image

IMAGE_PULL_POLICY=IfNotPresent make kube-deploy

• Create EnvoyExtensionPolicy resource

kubectl apply -f - << EOF
---
apiVersion: gateway.envoyproxy.io/v1alpha1
kind: EnvoyExtensionPolicy
metadata:
  name: my-wasm-1
  namespace: envoy-gateway-system
spec:
  targetRef:
    kind: Gateway
    name: eg
    group: gateway.networking.k8s.io
  wasm:
    - name: my_wasm_1
      code:
        type: Image
        image:
          url: oci://example.com/project/my-wasm:latest
          pullSecret:
            name: "some-secret-name"
      failOpen: true
      config:
        foo: value1
EOF

The resource should be created without issues

envoyextensionpolicy.gateway.envoyproxy.io/my-wasm-1 created

[zirain]

/retest

[zirain]

LGTM

cc @zhaohuabing

[zhaohuabing]

LGTM. Thanks!