[DOCS-8783] Updated Funnels and Pathways for Product Analytics

[rtrieu]

What does this PR do? What is the motivation?

• Updates the docs for Journeys, including new Funnels and Pathways UI
• Updates screenshots

Merge instructions

Merge readiness:

• Ready for merge

Merge queue is enabled in this repo. To have it automatically merged after it receives the required reviews, create the PR (from a branch that follows the <yourname>/description naming convention) and then add the following PR comment:

/merge

Additional notes

Needs PM review and confirmation before merging.

[github-actions]

Preview links (active after the build_preview check completes)

New or renamed files

• https://docs-staging.datadoghq.com/rtrieu/docs-8783-product-analytics-updates/product_analytics/journeys/pathways

Removed or renamed files (these should redirect)

• https://docs-staging.datadoghq.com/rtrieu/docs-8783-product-analytics-updates/product_analytics/journeys/sankey

Modified Files

• https://docs-staging.datadoghq.com/rtrieu/docs-8783-product-analytics-updates/product_analytics/
• https://docs-staging.datadoghq.com/rtrieu/docs-8783-product-analytics-updates/product_analytics/guide/rum_and_product_analytics
• https://docs-staging.datadoghq.com/rtrieu/docs-8783-product-analytics-updates/product_analytics/journeys/
• https://docs-staging.datadoghq.com/rtrieu/docs-8783-product-analytics-updates/product_analytics/journeys/funnel_analysis