Add CI YML example for Browser Performance Testing in CE
This MR adds an example CI YML for using Sitespeed.io into the CE repo.
It is slightly different than the EE one (gitlab-ee!3852 (merged)):
- It persists the full HTML report as an artifact, since we don't need the JSON report (EEP only feature).
- Includes a hard link to the EE repo for the full Browser Performance Testing feature.
Closes #41361 (closed)