Add RPCs to verify unknown numeric enums in path params and body

The current [VerifyEnum](https://github.com/googleapis/gapic-showcase/blob/f303df5681a64905996c66819828dcceb7b17ed9/schema/google/showcase/v1beta1/compliance.proto#L122) works great for asserting that unknown numeric enums should be passed in as numbers, but it's only for enums in query params. We can add two more RPCs to verify unknown numeric enums in path params and body.
The RPCs may look like this
```
rpc VerifyEnumPath(EnumResponse) returns (EnumResponse) {
option (google.api.http) = {
post: "/v1beta1/compliance/enum/{continent}"
};
}

rpc VerifyEnumBody(EnumResponse) returns (EnumResponse) {
option (google.api.http) = {
post: "/v1beta1/compliance/enum"
body: "*"
};
}
```