Scout guide - specify required permissions for API key

[Strift]

@macraig reported that customers struggled with Laravel Scout integration because the current guide does not give enough information about which permissions they should grant to their API key:

They would have liked to have a guide or page showing which permissions and API keys are needed for the Laravel Scout integration, especially since keys aren’t easy to update and can’t be updated via the UI.

Tasks

• [ ] Rewrite /guides/back_end/laravel_scout.mdx so it uses an API key instead of the master key
  • If possible, probably best if we recommend using the two default API keys (admin and search)