postgresql: Initial parser implementation

This adds a protocol parser for the PostgreSQL protocol and a new
postgresql.log similar to the existing mysql.log.

This should be considered preliminary and hopefully during 7.1 and 7.2
with feedback from the community, we can improve on the events and logs.
Even if most PostgreSQL communication is encrypted in the real-world, this
will minimally allow monitoring of the SSLRequest and hand off further
analysis to the SSL analyzer.

This originates from github.com/awelzel/spicy-postgresql, with lots of
polishing happening in the past two days.

NEWS

@@ -28,6 +28,22 @@ Breaking Changes
 New Functionality
 -----------------
 
+- Zeek now includes a PostgreSQL protocol analyzer. This analyzer is enabled
+  by default. The analyzer's events and its ``postgresql.log`` should be
+  considered preliminary and experimental until the arrival of Zeek's next
+  long-term-stable release (8.0).
+
+  If you observe unusually high CPU consumption or other issues due to this
+  analyzer being enabled by default, the easiest way to disable it is via the
+  ``Analyzer::disabled_analyzers`` const as follows:
+
+	redef Analyzer::disabled_analyzers += {
+		Analyzer::ANALYZER_POSTGRESQL,
+	};
+
+  If you observe PostgreSQL traffic in your environment, please provide feedback
+  about the analyzer and structure of the new log.
+
 * The LDAP analyzer now supports handling of non-sealed GSS-API WRAP tokens.
 
 * StartTLS support was added to the LDAP analyzer. The SSL analyzer is enabled