Implement Web Vitals

[ankur22]

This follows on from the POC #657.

We want to implement the Web Vitals properly into xk6-browser. The following are the sub issues for this issue:

• Add the Web Vital JS code with the existing injected script. #690 (MUST) — v0.9.0
• Remove First Meaningful Paint browser metric #837 (MUST) — v0.9.0
• Evaluate browser metrics against webvital metrics #831 (MUST) — v0.9.0

[ankur22]

Moving this back to the backlog for now. The must have tasks have been completed.

[ankur22]

Removed the following issues from this issue:

• Parse and print webvital summary #691 (Nice-to-have) — v0.10.0

This isn't a priority since users haven't asked for this and there are workaround to this where they could retrieve the data and work with it however they wish.

• Ensure that Web Vitals are aggregated based on frame and sub frame #692 (Nice-to-have) — v0.10.0

This is likely to be solved in the future with the work on the timeline.