Add PostgreSQL REPL implementation

[gabrielcorado]

Part of #44956 (RFD 0181)

This PR introduces the PostgreSQL REPL implementation following the RFD definition, which will be used as a client to access PostgreSQL instances through WebUI. It works like a terminal emulator (implemented by golang.org/x/term library) and will be used with the WebUI terminal (like WebUI SSH sessions).

Note

This PR only includes the REPL implementation. The web handlers and WebUI changes will be done in different PRs.

For this first release of the REPL, we're not including informational commands (such as \d or \dt). These commands will require better testing across different PostgreSQL versions and will be introduced in later versions.

[greedy52]

First pass. Overall logic looks good to me.

A few things i wonder if we could do (not immediately but maybe after MVP):

1. common REPL so it can be used for other protocols like MySQL
2. test postgres repl (or even do this through the webapi websocket) in E2E test (or testcontainers) against real RDS/Postgres

[greedy52]

write non-empty reply before exit?

[gabrielcorado]

@greedy52

common REPL so it can be used for other protocols like MySQL

We could do this in the future (when we introduce another database). However, it is a bit difficult to identify which part we can reuse right now.

test postgres repl (or even do this through the webapi websocket) in E2E test (or testcontainers) against real RDS/Postgres

I'll add the integration and E2E tests after we have both parts (web handler and REPL) ready/merged. So we can thoroughly test their usage against the databases.