Setup for dashboards - Router + Files based Dashboards

What does this MR do and why?

• Introduces Vue Router for the Product Analytics Dashboards
• Loads the list of internal dashboards from file
• Loads individual dashboards from file

Screenshots or screen recordings

How to set up and validate locally

• Activate the product analytics feature flag echo "Feature.enable(:product_analytics_internal_preview)" | rails c

• Navigate to http://localhost:3000/flightjs/Flight/-/product_analytics/dashboards

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.

Closes #377851 (closed)