Add service worker to permanently-cache some artifacts

[menduz]

The routes that should be locally cached forever are:

• https://peer*.decentraland.org/content/contents/*
• https://content-assets-as-bundle.decentraland.org/**
• https://cdn.decentraland.org/**

This is possible using the CacheStorage API available in service workers

[aixaCode]

decentraland/unity-renderer#3802