Enable sampling profiler for better `bootup-time` attribution

**Feature request summary**
Enable the `disabled-by-default-v8.cpu_profiler` trace category.

**What is the motivation or use case for changing this?**
In https://github.com/GoogleChrome/lighthouse/pull/7059#issuecomment-461924036 we discussed enabling the sampling profiler to improve the attribution of scripts in `bootup-time` audit. Additionally, one of our smoketests that tests attribution was thought to only require async stacks, but turns out also needs sampling profiler now due to other restructuring of tasks.

https://github.com/GoogleChrome/lighthouse/blob/b4d9107263db043e6f776892571e4b9575c78a42/lighthouse-cli/test/smokehouse/tricky-metrics/expectations.js#L63-L71

**How is this beneficial to Lighthouse?**
Improved attribution of scripts and the elimination of "Other" as a large category in `bootup-time` results.