pgsql: add subprotocol-states
In order to keep adding PostgreSQL support in Suricata, cover sub-protocol states:
- Extended query
- COPY operators
- Function call
Even though PostgreSQL refers to those as sub-protocols, to Suri, they're more like sub-states, where we'll expect to parse different sets of messages.
These could then be used in some Detect situations as well.
More details about each sub-protocol can be found in the protocol official documentation: https://www.postgresql.org/docs/13/protocol-flow.html