Stable interfaces

[sfc-gh-rchen]

Implements "stable interface" idea Andrew began here to allow processes with differing protocol versions to communicate their protocol versions with each other. This commit adds a stable ProtocolInfoRequest endpoint that can be used to get a processes' protocol version across protocol versions. Later, this endpoint can be used in the Multi-version client, for example, to only run clients which are compatible with the server.

This commit also adds/modifies simulator code necessary to test the stable endpoint idea. This involves adding a new mapping in Sim2 which maps process to protocol version, modifying calls to simulatedFDBDRebooter to start one process with a specified protocol version, and adding an option in test files to modify the protocol version.

Currently, this commit only supports testing one process with a different protocol version.

#3966

[xumengpanda]

Can you explain in the PR on

1. what the problem it solves;
2. definition of stable interfaces;
3. high-level design idea;

An example of the PR explanation is #3856.

A good PR description can help people to better understand the implementation.

[sfc-gh-anoyes]

Can you explain in the PR on

1. what the problem it solves;

2. definition of stable interfaces;

3. high-level design idea;

An example of the PR explanation is #3856.

A good PR description can help people to better understand the implementation.

I can follow up with more design details. For now this is a work in progress draft PR

[AlvinMooreSr]

@fdb-build test this please