Fixes https://emqx.atlassian.net/browse/EMQX-10629
During health checking, we check whether tables in the SQL statement
exist. Such check was done by asking the backend to parse the
statement using a named prepared statements. Concurrent health checks
could then result in the error:
```erlang
{error,{error,error,<<"42P05">>,duplicate_prepared_statement,<<"prepared statement \"get_status\" already exists">>,[{file,<<"prepare.c">>},{line,<<"451">>},{routine,<<"StorePreparedStatement">>},{severity,<<"ERROR">>}]}}
```
This could lead to an inconsistent state in the driver process, which
would crash later when a message from the backend (`READY_FOR_QUERY`, "idle"):
```
2023-07-24T13:05:58.892043+00:00 [error] Generic server <0.2134.0> terminating. Reason: {'module could not be loaded',[{undefined,handle_message,[90,<<"I">>,...
```
Added calls to `epgsql:sync/1` for functions that could return
`{error, sync_required}`.
Also, redundant calls to `parse2` were removed to reduce the number of requests.
Thales Macedo Garitezi