[Epic] Refactor pgsrv

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Description

I'm seeing a trend in a few issues regarding pgsrv, and so I'm taking the liberty to spawn an epic. Essentially, pgsrv is a critical component as without it, nothing in glaredb can be accessed by an external user. The main problems we have are:

• lack of health check
• lack of core/critical tests
• lack of shared machinery with the "Cloud Client": https://github.com/GlareDB/glaredb/tree/main/crates/cloud

Implementing these things should make future implementations in pgsrv easier, and give it access to shared machinery.

Rationale

A hard blocker for beta is terminating ssl in pgsrv. Before we implement that, we want to be confident in the implementation (including tests).

Issues (In an attempted priority order)

• Liveness check for pgsrv #250
• pgsrv: Add tests to ensure appropriate parsing #100
• Revisit error handling in pgsrv #217
• Terminate SSL connections in pgsrv proxy #210
• Chore: Move pgsrv to its own binary #367

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We're not focusing on pgsrv much right now, not doing the sep binary thing - closing epic (but leaving open tickets open)