Add GA4 tracking with GDPR cookie consent banner

[khuyentran1401]

Description

Adds Google Analytics (GA4) tracking to the skillsctl docs site, gated behind a GDPR-compliant cookie consent banner. GA4 sets cookies that track visitors, so EU privacy law requires opt-in consent before any tracking fires.

What does this implement/fix?

• New feature (non-breaking change which adds a feature)

What's included

• Analytics: GA4 via the shared Nebari property.
• Consent: opt-in banner gating all tracking.
• Privacy-by-default: no cookies set until the user accepts.

Expected behavior

• On first visit, a consent banner appears in the bottom-right corner and no GA4 cookies are set.
• Two categories are exposed: Strictly necessary (always on) and Analytics (opt-in, controls GA4).
• Clicking Accept all enables GA4 tracking and remembers the choice.
• Clicking Reject all keeps tracking disabled; the banner does not reappear.
• Users can reopen Manage preferences later to change their choice, and GA4 updates immediately.