ch: support connecting to a specified instance for ap

[zyguan]

Signed-off-by: zyguan zhongyangguan@gmail.com

Add the following three options to ch run, which overwrite conn-params, host, port when opening db for analytical processing.

      --ap-conn-params string   Connection parameters for analytical processing
      --ap-host string          Database host for analytical processing
      --ap-port int             Database port for analytical processing