jsonpath is not supported #635

• asyncpg version: 0.21.0
• PostgreSQL version: 12.2
• Do you use a PostgreSQL SaaS? If so, which? Can you reproduce
  the issue with a local PostgreSQL install?: no
• Python version: 3.7.9
• Platform: OpenBSD
• Do you use pgbouncer?: no
• Did you install asyncpg with pip?: with poetry
• If you built asyncpg locally, which version of Cython did you use?:
• Can the issue be reproduced under both asyncio and
  uvloop?: uvloop is used

Quering jsonb_path_query with jsonpath raises NotImplementedError:
unhandled standard data type 'jsonpath' (OID 4072)

Here is original query:

SELECT jsonb_path_query(data, :jsonpath) FROM reference_data WHERE reference_id=:id LIMIT 20

jsonpath is a string.