Add more compatibility tests

[discord9]

What type of enhancement is this?

User experience

What does the enhancement do?

Upgrade compatibility is a vital part of user experience, and more upgrade compatibility tests to make sure of smooth upgrade from, say, last three major version should be ensured. There is currently some upgrade compatibility tests in ./tests/upgrade-compat and can be run by the following command(require docker):

cargo sqlness -c $(pwd)/tests/upgrade-compat --store-addrs "0.0.0.0:2379" --setup-etcd 

More tests can be added to ensure upgrade compatibility.

Implementation challenges

possible challenges are:

• thoroughly test every possible options that can be set using sql(Features can be added to sqlness runner to support testing HTTP API, but is not in the scope of this issue)
• add upgrade compatibility tests to CI for nightly run or weekly run