Update the mobile preset

**Feature request summary**
Can the mobile preset speed be increased, it's an issue that has been raised and dismissed before

**What is the motivation or use case for changing this?**
The mobile landscape has changed dramatically over the last 3 years. The 85th percetile has to be higher than 1.6mbps

https://infrequently.org/2024/01/performance-inequality-gap-2024/#test-device-recommendations now suggests a Samsung Galaxy A51 or Google Pixel 4a as the benchmark, and a P75 estimate of 7.2Mbps down, 1.4Mbps up, and 94ms RTT.

**How is this beneficial to Lighthouse?**
It will bring the audit more in line with real world averages