docs: Add comprehensive Nix cache documentation

[joereg4]

Fixes #1622

Description

Adds comprehensive documentation for the Nix binary cache system used in the Supabase PostgreSQL project.

Changes

• Created nix/docs/nix-cache.md with comprehensive cache documentation
• Updated nix/docs/README.md to include cache docs in navigation
• Updated nix/mkdocs.yml to add cache docs to MkDocs navigation
• All tests pass (nix flake check -L)

Closes #1622"

[joereg4]

I noticed the CI failed due to missing AWS credentials. Are contributors supposed to receive credentials or should those steps skip in forks / PRs?

[joereg4]

Hello @samrose,

I'm a new contributor working on a PR for issue #1622 (Nix cache documentation). I've encountered the AWS credentials CI failure on my fork's PR and wanted to reach out for some guidance.

I've observed that the run-testinfra jobs fails with DEV_AWS_ROLE credential errors on fork PRs. This appears to be GitHub's security model preventing forks from accessing repository secrets. Looking through PRs and I do see this is impacting others as well.

All my local and other CI tests pass and the code changes are documentation-focused (new nix-cache.md file).

Since you are the #1 contributor, what's the best way forward for contributors facing this CI limitation? Should I wait for a maintainer to manually review/approve the AWS tests, or is there something else I should be doing?

[joereg4]

@steve-chavez Good afternoon, trying to resolve the issue you posted regarding documentation. I'm stuck with the run-testinfra jobs failing with DEV_AWS_ROLE credential errors. Any suggestions?

[steve-chavez]

@steve-chavez Good afternoon, trying to resolve the issue you posted regarding documentation. I'm stuck with the run-testinfra jobs failing with DEV_AWS_ROLE credential errors. Any suggestions?

Unfortunately I'm not acquainted with that part of the codebase. We'll have to wait for input from Sam or other core contributors.

[samrose]

Will review ASAP thank you!

[joereg4]

Updated to sync with latest develop branch. This PR now includes:

• Original documentation for Nix cache (addresses Nix cache is not documented #1622)
• Latest upstream changes (ansible modernization, WAL-G fixes, supautils v3.0.0, postgres_fdw tests)

All 45 regression tests and 34 migration tests passing locally. Documentation builds successfully.

[joereg4]

@samrose I'm sure people are busy, was hoping to get this first contribution done since it was only documentation. Have another issue ready to solve but want to clear this one first.