Optimize network bandwidth usage

1. Generate for each response an ETag header based on the MD5 of its content. If the client sent the If-Not-Match header, compare its value against the ETag header of the generated response. If they match, send status code 304 Not Modified without body, otherwise normal response. It will send only the HTTP body if the data of the client is stale.
2. Use the Brotli compression algorithm as standard with GZip as fallback https://github.com/fullonic/brotli-asgi