sql: support COPY from stdin binary

[maddyblue]

The binary mode is used by https://github.com/jackc/pgx and would be nice to be able to use as an alternative to lib/pq's funky COPY support that mandates a transaction.

From: https://www.postgresql.org/docs/9.2/sql-copy.html

The binary format option causes all data to be stored/read as binary format rather than as text. It is somewhat faster than the text and CSV formats, but a binary-format file is less portable across machine architectures and PostgreSQL versions. Also, the binary format is very data type specific; for example it will not work to output binary data from a smallint column and read it into an integer column, even though that would work fine in text format.

The binary file format consists of a file header, zero or more tuples containing the row data, and a file trailer. Headers and data are in network byte order.

[rafiss]

See also #41608 for additional COPY syntax

[solongordon]

Sending to Bulk I/O backlog since we don't have COPY expertise on SQL Features. Would you be able to evaluate how difficult this implementation is? Per @vy-ton we want to shore up features required by pgx so that we can recommend it to customers.

[dt]

@mjibson which usage were you thinking of? the file upload stuff?

[maddyblue]

COPY BINARY is just what pgx hard codes as its COPY implementation. Nothing to do with IMPORT or file uploads.

[dt]

Ah, okay, so this is about supporting the binary format modifier to the SQL COPY .. FROM statement, which gets planned as an INSERT? Got it -- I don't think that overlaps with any bulk-io stuff then -- we just use COPY support, but didn't implement or maintain it.