docs: add missing RLS step to Next.js tutorial (#82714)
## What
This PR updates
`examples/with-supabase/components/tutorial/fetch-data-steps.tsx` to
include a missing step about enabling Row Level Security (RLS) and
creating a simple read policy for the `notes` table.
Fixes: #82218
## Why
Currently, the tutorial shows how to:
- create a `notes` table
- insert data
- query data from Next.js
However, since RLS is enabled by default in Supabase, new users will get
`permission denied` errors when querying data unless they configure
policies.
The official Supabase Next.js quickstart docs already mention this:
https://supabase.com/docs/guides/getting-started/quickstarts/nextjs
Adding this step will help newcomers understand why RLS is required and
how to set it up.
## Changes
- Added a new `<TutorialStep>` in `fetch-data-steps.tsx`:
- Explains that RLS is enabled by default
- Shows SQL snippet to enable RLS + create a public read policy
- Links to the Supabase RLS docs
## Checklist
- [x] Added RLS tutorial step
- [x] Verified formatting matches other tutorial steps
- [x] Added links to relevant Supabase docs
Co-authored-by: Joseph <joseph.chamochumbi@vercel.com>
