release-22.1: clisqlshell: implement COPY ... FROM STDIN for CLI

[otan]

Backport 1/1 commits from #79629.

/cc @cockroachdb/release

Release justification: critical improvement to 22.1

---

Resolves #16392

Steps:

• Add a lower level API to lib/pq for use.
• Add some abstraction boundary breakers in clisqlclient that allow a
  lower level handling of the COPY protocol.
• Altered the state machine in clisqlshell to account for copy.

Release note (cli change): COPY ... FROM STDIN now works from the
cockroach CLI. It is not supported inside transactions.

[blathers-crl]

Thanks for opening a backport.

Please check the backport criteria before merging:

• Patches should only be created for serious issues or test-only changes.
• Patches should not break backwards-compatibility.
• Patches should change as little code as possible.
• Patches should not change on-disk formats or node communication protocols.
• Patches should not add new functionality.
• Patches must not add, edit, or otherwise modify cluster versions; or add version gates.

If some of the basic criteria cannot be satisfied, ensure that the exceptional criteria are satisfied within.

• There is a high priority need for the functionality that cannot wait until the next release and is difficult to address in another way.
• The new functionality is additive-only and only runs for clusters which have specifically “opted in” to it (e.g. by a cluster setting).
• New code is protected by a conditional check that is trivial to verify and ensures that it only runs for opt-in clusters.
• The PM and TL on the team that owns the changed code have signed off that the change obeys the above rules.

Add a brief release justification to the body of your PR to justify this backport.

Some other things to consider:

• What did we do to ensure that a user that doesn’t know & care about this backport, has no idea that it happened?
• Will this work in a cluster of mixed patch versions? Did we test that?
• If a user upgrades a patch version, uses this feature, and then downgrades, what happens?

[cockroach-teamcity]

This change is 

[knz]

i'm not keen on backporting a dependency on a forked lib/pq if we can merge the change upstream

[otan]

latest lib pq changes introduced something somewhat unstable due to the cancel changes (when I updated last year a bunch of tests failed) so I'd rather use the fork. but maybe I'm misremembering.. I feel the smaller set of changes is safer as a backport so I'd rather do this for now.

[otan]

eh ill give it a shot, but if there are unrelated failing tests ill revert