Chore: simplify with-supabase example (#57562)
### What?
[1] Simplify example
[2] Refactor `delete` method to use `cookies.set`
### Why?
[1] Make it easier to follow
[2] Fix build errors
### How?
[1] Adding comments and abstracting code into helper functions
[2] Setting cookie to empty value when removed
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Co-authored-by: Lee Robinson <me@leerob.io>
