Add GoTrue nix files + Initial setup

[J0]

What kind of change does this PR introduce?

Adds GoTrue nixfiles. k6 files to follow up in a subsequent PR

What is the current behavior?

Benchmarks exist for Postgrest + Postgres(Supabase flavoured)

What is the new behavior?

Benchmarks for KPS, completing the trinity.

Additional context

Add any other context or screenshots.