Updating macOS development readme with some gotchas that I ran into
while getting setup.
- Linked to collab readme because that contained the steps to setup the
postgres database so integration tests pass
- Added section under troubleshooting. Recommending `cargo-nextest`
since the CI uses it and it got me past the failures I was seeing.

Release Notes:

- N/A

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Co-authored-by: KyleBarton <kjbarton4@gmail.com>