Enhanced Aggregates Capabilities in Sentry Logs

### Problem Statement

We’ve been reviewing Sentry’s capabilities and identified several limitations that make it difficult to perform product-level analysis, even though the underlying data exists. While Sentry is excellent for error tracking and performance monitoring, the following features would significantly improve its utility for product analytics:
- Support for calculating percentages of users who go from A → B vs A → X, based on existing navigation and interaction logs.
- Average Time per Page. Ability to compute time differences between navigation spans to measure time-on-page.
- Ability to identify the first navigation span in each trace for better understanding of user entry points.

### Solution Brainstorm

_No response_

### Product Area

Dashboards

Start by reviewing Sentry's dashboard aggregation capabilities and the existing navigation and interaction logs described in the issue. Done would mean defining and implementing support for user-path percentages, time per page, and first-navigation-span analysis.

Written by the indexing model from the issue text.