Enhance sqlness harness to accept a connection string

[waynexia]

What problem does the new feature solve?

Our sqlness harness (cargo sqlness) will start its db process for testing. It's helpful to make it able to accept a connection string and run cases on a remote db instance.

E.g.:

cargo sqlness --host 127.0.0.1 --port 3306

What does the feature do?

Add two new cli options --host/-h and --port/-p to sqlness cli. And skip starting the db process if a remote address is provided.

Notice that the RESTART command won't work under this mode. We can simply ignore it and emit a log

Implementation challenges

No response