Set Forbidden as the response status reason

[regadas]

Describe the solution you'd like
Hello 👋

Recently while integrating gatekeeper I noticed that a denied admission webook response will look somewhat like this:

Message and Reason kinda have the same info.

errors.StatusError{
    ErrStatus:v1.Status{
        TypeMeta:v1.TypeMeta{Kind:\"\", APIVersion:\"\"},
        ListMeta:v1.ListMeta{
            SelfLink:\"\",
            ResourceVersion:\"\",
            Continue:\"\",
            RemainingItemCount:(*int64)(nil)},
        Status:\"Failure\",
        Message:\"admission webhook \\\"validation.gatekeeper.sh\\\" denied the request: [enforce-resource-quota] resource exceeded cpu quota\",
        Reason:\"[enforce-resource-quota] resource exceeded cpu quota\",
        Details:(*v1.StatusDetails)(nil),
        Code:403}
}

I guess this is generally ok! However, if one is using "k8s.io/apimachinery/pkg/api/errors" to determine the type of error we are out of luck since it relies on the Reason property.

Given the above example:

errors.IsForbidden(err) // False

I suggest a small change in the StatusError and give Reason the proper description keeping Message as the human-readable description of this operation.

errors.StatusError{
    ErrStatus:v1.Status{
        TypeMeta:v1.TypeMeta{Kind:\"\", APIVersion:\"\"},
        ListMeta:v1.ListMeta{
            SelfLink:\"\",
            ResourceVersion:\"\",
            Continue:\"\",
            RemainingItemCount:(*int64)(nil)},
        Status:\"Failure\",
        Message:\"admission webhook \\\"validation.gatekeeper.sh\\\" denied the request: [enforce-resource-quota] resource exceeded cpu quota\",
        Reason:\"Forbidden\",
        Details:(*v1.StatusDetails)(nil),
        Code:403}
}

Anything else you would like to add:

Here's a PR with the proposed change. #1692