Fix: Add Yarn installation and correct Redis host configuration in init.sh

[3aluw]

This PR closes #13
This PR fixes two issues in the init.sh setup script that were preventing a smooth ERPNext/Frappe setup.

Changes made

1. Install Yarn automatically

   • Added npm install -g yarn after Node.js is set up.
   • Ensures bench build works without manual installation.

2. Fix Redis host configuration

   • Removed the :6379 port suffix from Redis host values.
   • Correctly uses only the hostname (redis-cache, redis-queue, redis-socketio), since bench set-redis-*-host expects just the hostname.

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Before

bench set-redis-cache-host redis-cache:6379
bench set-redis-queue-host redis-queue:6379
bench set-redis-socketio-host redis-socketio:6379

After

npm install -g yarn

bench set-redis-cache-host redis-cache
bench set-redis-queue-host redis-queue
bench set-redis-socketio-host redis-socketio

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