[DOCS-8783] Product Analytics UI changes

[rtrieu]

What does this PR do? What is the motivation?

This updates images and text according to the updated Product Analytics UI:

• Filters have been moved to the left
• New Journeys icon
• "Sankey" is now "Pathways"
• Reordered Pathways so that it's first, followed by Funnel Analysis and Conversion, to match the UI
• Also added a page for Conversion

Merge instructions

• [x] Please merge after reviewing

Additional notes

[github-actions[bot]]

Preview links (active after the build_preview check completes)

New or renamed files

• https://docs-staging.datadoghq.com/rtrieu/product-analytics-ui-changes/product_analytics/journeys/conversions
• https://docs-staging.datadoghq.com/rtrieu/product-analytics-ui-changes/product_analytics/journeys/pathways

Removed or renamed files (these should redirect)

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

Modified Files

• https://docs-staging.datadoghq.com/rtrieu/product-analytics-ui-changes/dashboards/widgets/sankey
• https://docs-staging.datadoghq.com/rtrieu/product-analytics-ui-changes/product_analytics/
• https://docs-staging.datadoghq.com/rtrieu/product-analytics-ui-changes/product_analytics/guide/rum_and_product_analytics
• https://docs-staging.datadoghq.com/rtrieu/product-analytics-ui-changes/product_analytics/journeys/
• https://docs-staging.datadoghq.com/rtrieu/product-analytics-ui-changes/product_analytics/segmentation/