Proposal: disallow unsigned integers for istio.* protobuf namespace

[wora]

I would like to formally suggest to disallow unsigned integers for istio.* protobuf namespace for the following reasons.

• If we allow unsigned integers, people inevitably will use mismatched signed and unsigned types for the same concept, such as network port. It leads to undefined behavior in different languages like C/C++/Java.
• istio attributes only support signed integer. Adding unsigned integer increase system complexity for no real benefit.
• Istio namespace is mostly for configs. The workflow for config is like this: proto schema => documentation => human => yaml => tools => proto config. The critical step is human => yaml. It is very unlikely humans can reliably remember the data types. And mismatch types will confuse users in practice.
• Many important systems, like Java, Stackdriver monitoring, don't support unsigned types at all. If we want to build a generic system, it is better to avoid this unnecessary risk.
• Google have discouraged unsigned integers for over a decade and we have not seen much downside across wide range of products.

To avoid unnecessary complexity to the system, I think we should avoid unsigned type for istio namespace.