Mark status.endpoint as optional in AKSCluster

[turkenh]

Description of your changes

While running crossplane conformance tests, I observed following failure:

=== RUN   TestPackage/DeploysConformantCRDs/AKSCluster
    provider_test.go:436: version "v1alpha3" OpenAPI schema: -want, +got:
          &v1.JSONSchemaProps{
            ... // 1 ignored and 25 identical fields
            AnyOf: nil,
            Not:   nil,
            Properties: map[string]v1.JSONSchemaProps{
                ... // 2 identical entries
                "metadata": {Type: "object"},
+ go-junit-report
                "spec":     {Type: "object", Properties: {"deletionPolicy": {Type: "string", Enum: {{Raw: {0x22, 0x4f, 0x72, 0x70, ...}}, {Raw: {0x22, 0x44, 0x65, 0x6c, ...}}}}, "providerConfigRef": {Type: "object", Required: {"name"}, Properties: {"name": {Type: "string"}}}, "writeConnectionSecretToRef": {Type: "object", Required: {"name", "namespace"}, Properties: {"name": {Type: "string"}, "namespace": {Type: "string"}}}, ...}},
                "status": {
                    ... // 1 ignored and 19 identical fields
                    MaxProperties: nil,
                    MinProperties: nil,
        -           Required:      nil,
        +           Required:      []string{"endpoint"},
                    Items:         nil,
                    AllOf:         nil,
                    ... // 18 identical fields
                },
            },
            AdditionalProperties: nil,
            PatternProperties:    nil,
            ... // 12 identical fields
          }

It does not make sense to have a field as "required" in the status of a custom resource since that is not set by the user rather managed by the provider controller.

I have:

• Read and followed Crossplane's contribution process.
• Run make reviewable test to ensure this PR is ready for review.

How has this code been tested

• Deploy provider-azure
• Create an AKSCluster resource
• Verify it reports ready with valid status