Install psycopg2 based on platform

[mikealfare]

resolves #50

Problem

psycopg2 takes a long time to build, and needs additional os dependencies, so it's not great for development. psycopg2-binary solves this problem. However, psycopg2-binary has some performance issues due to being build platform-agnostic, so it's not great for production.

Solution

• make the assumption that most production workloads are hosted on linux and most development workloads are hosted on macos/windows
• identify desired version of psycopg2 based on host platform

Side effect:

• remove partial parsing tests; they started failing and they don't use any dbt-postgres or dbt-adapters functionality

Benefits

• remove hatch build hooks and associated complexities
• gain standard automation tools, e.g. dependabot alerts
• remove need to rely on an environment variable at runtime

Costs

• there will be development users on linux and production workloads on windows (likely Windows Server)
• document workaround for edge cases on how to get the other

Checklist

• I have read the contributing guide and understand what's expected of me
• I have run this code in development and it appears to resolve the stated issue
• This PR includes tests, or tests are not required/relevant for this PR
• 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

[colin-rogers-dbt]

Suggested change

	body: Determine `psycopg2` based on `platform_system` (Linux or other)
	body: Determine `psycopg2` based on `platform_system` (Linux or other), remove usage of `DBT_PSYCOPG2_NAME` environment variable