chore: update default script examples

[peterschretlen]

What this PR does / why we need it:

This PR updates the default scripted and browser examples to:

• Use quickpizza login as the example for both scripts
• Advertise k6 studio for recording browser scripts
• Advertise secrets management
• Modernize by replacing fail with expect (assertions library)

Which issue(s) this PR fixes:

Fixes https://github.com/grafana/synthetic-monitoring/issues/358

My main concern is this makes the default scripts longer and harder to read.

Scripted Before

Scripted After

Browser Before

Browser After

[github-actions]

Script size changes

Name	+/-	Main	This PR	Outcome
[module.js]	+0.08%	2,386.30 kB	2,388.11 kB	✅
[datasource/module.js]	=	24.68 kB	24.68 kB	✅

Totals

Name	+/-	Main	This PR	Outcome
[Scripts]	+0.07%	2,410.98 kB	2,412.79 kB	✅
[Non-script Assets]	=	2,587.82 kB	2,587.82 kB	✅
[All]	+0.04%	4,998.80 kB	5,000.61 kB	✅

Generated by 🚫 dangerJS against c6ac99d