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

[blakeli0]

The current VerifyEnum 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: "*"
    };
  }

[callmetushar123]

@vchudnov-g can you please assign me this issue? I think would be a good first issue for me as I am new to open source contributing