Browser: Missing warning boxes

[inancgumus]

The browser team uses the BWIPT marker to add a warning box for a missing/problematic feature.

• This feature is used to work in the older k6 docs.
• The old k6 docs used this code to generate the warning box.
• The warning box is clickable and redirects to a relevant issue in the xk6-browser repository.

Hopefully, this feature might be added back in using Hugo's shortcodes 🤞

Before

After

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### Tasks
- [ ] grafana/website#19916
- [ ] #1599

[heitortsergent]

@jdbaldry is this something you could help us with? I was wondering if we should keep track of this here or on the website repo.

[heitortsergent]

@inancgumus do you think we can close this issue? I think updating it to use Grafana Labs colors can be separate from this.

[inancgumus]

@heitortsergent Yep, we're all good 👍