feat: postgres example

[chesedo]

A working example and e2e test for connecting to postgres

[brokad]

I've added a couple features for making this easier to track:

• Randomized port attributions so that tests can run in //
• The postgres test runs with the api docker image (this will make it pick up hygiene issues easier)
• Capture of the stdout/stderr of spawned things along with prefixing and color differences for tracking it all

AFAICT, the tests fail for two reasons:

• The users.toml path is brittle, and does not exist in the docker container
• The unveil-service version mismatch (between crates.io and local) which causes the example to build locally, but not server-side

Then:

• The tests may still fail in CI if we don't add the corresponding dummy auth tokens while they run there

[brokad]

@chesedo legend