Streamline pgmq-rs ext client queue creation behaviour

[v0idpwn]

Currently, create, create_partitioned, create_non_partitioned and create_unlogged return Result<Boolean, Error>, and claim to return false if the queue already existed, but create, create_non_partitioned and create_unlogged return true independent from the queue existing or not.

[v0idpwn]

The extension-less client returns Result<(), Error>, which is simpler and probably as useful, since the inforrmation about the queue being new or not is not that relevant.

[ChuckHend]

Also a bug in pgmq-rs, should return False when queue already exists.

[ChuckHend]

Also a bug in pgmq-rs, should return False when queue already exists.

decided to ignore this and return unit to be consistent with all create functions