Add tracing for connecting to postgres

[KyleAMathews]

This is a difficult to debug area where both the server authors and users would like detailed information about what happened when a connection to postgres fails.

We should add a span for the connection process with all provided information and sub-spans for any interesting subroutines. And capture all errors.

[alco]

Could you clarify about the "span for the connection process"? Is it about tracing the connection initialisation, i.e. from the moment Electric opens a connection to Postgres and up until the point it either succeeds or fails?

[KyleAMathews]

yeah exactly, the initialization. Also reconnects, retries, etc.

[balegas]

We'll work on this once #1762 is in.