Support of "Property Graph Query" (PGQ) language

[Seddryck]

PGQ is a SQL-like query language for property graph data structures that consist of vertices that are connected to other vertices by edges, each of which can have key-value pairs (properties) associated with them.

Sometimes also named "Property Graph Query Language" (PGQL)

Based on Oracle research: https://github.com/oracle/pgql-lang
Should be available in an extension of DuckDB: https://github.com/cwida/duckdb-pgq