feat: add connection test case

tests/script/general/connection/connection.sim

+system sh/stop_dnodes.sh
+system sh/deploy.sh -n dnode1 -i 1
+system sh/cfg.sh -n dnode1 -c wallevel -v 0
+system sh/exec.sh -n dnode1 -s start
+sleep 3000
+sql connect
+
+print ============= step1
+sql close
+print close1
+sql connect
+
+print ============= step2
+sql close
+sql connect
+
+print ============= step3
+sql close
+sql connect write
+
+system sh/exec.sh -n dnode1 -s stop -x SIGINT
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