feat: Notices on transactions

[scsmithr]

Emit notices on transaction commands warning about our incomplete transaction support.

psql:

sean@Seans-Air glaredb % psql postgres://localhost:6543
psql (15.4, server 15.1)
Type "help" for help.

sean=> begin;
WARNING:  GlareDB does not support proper transactional semantics. Do not rely on transactions for correctness. Transactions are stubbed out to enable compatability with existing Postgres tools.
BEGIN
sean=> 

CLI (colorful):

Some pg protocol tests added to assert the notices.

[tychoish]

do we want to write to stderr?

[scsmithr]

We could. Since this is in the interactive portion, I don't know that it matters. But we could also move this to the execute func and eprintln there.

[tychoish]

stderr feels right for this kind of thing, (if only because it makes it easier to write scripts.) but this doesn't need to block.

[scsmithr]

updated