Rework record/replay to record at the database connection level.

[peterallenwebb]

Problem

Our previous approach to recording DWH interaction short-circuited a large amount of our own code upon replay. This caused problems with replay behavior, and was also conceptually difficult to reason about.

Solution

Record and replay at a different level of abstraction, cleanly separating dbt code from 3rd party code.

Checklist

• [x] I have read the contributing guide and understand what's expected of me
• [x] I have run this code in development, and it appears to resolve the stated issue
• [x] This PR includes tests, or tests are not required/relevant for this PR
• [x] This PR has no interface changes (e.g. macros, cli, logs, json artifacts, config files, adapter interface, etc.) or this PR has already received feedback and approval from Product or DX

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