[11.x] Add missing .env values for Reverb configuration

[takielias]

This PR addresses the missing .env configuration values for Reverb in the broadcasting documentation. The current example references import.meta.env.VITE_REVERB_APP_KEY, import.meta.env.VITE_REVERB_HOST, and other related variables, but the corresponding .env file example only includes pusher related values.

I have added the necessary Reverb-specific .env variables:

VITE_APP_NAME="${APP_NAME}" VITE_REVERB_APP_KEY="${VITE_PUSHER_APP_KEY}" VITE_REVERB_HOST="${VITE_PUSHER_HOST}" VITE_REVERB_PORT="${VITE_PUSHER_PORT}" VITE_REVERB_SCHEME="${VITE_PUSHER_SCHEME}" VITE_REVERB_APP_CLUSTER="${VITE_PUSHER_APP_CLUSTER}"

Including these variables ensures that users configuring Reverb for their Laravel Echo setup have a complete and accurate .env file to work with. This update helps prevent potential confusion and setup issues.