Bump sitespeed to 8.x, update plugin for support

Problem to solve

For Browser Performance Testing in Auto DevOps we are currently pinned to SiteSpeed 6.x, and the current release is now up to 8.x. We should bump AutoDevOps to utilize the latest features.

Target audience

Further details

Proposal

There looks to be an issue with the current exporter and 8.x, but a great community member has already provided an MR. We should validate and them merge to enable us to support 8.x. MR: gl-performance!3 (merged)

Once the plugin supports 8.x, we should then bump the pinned version of SiteSpeed in the AutoDevOps template.

Documentation

What does success look like, and how can we measure that?

What is the type of buyer?

(Which leads to: in which enterprise tier should this feature go see https://about.gitlab.com/handbook/product/pricing/#four-tiers )

Links / references