Add New Trace Explorer + Span-based Metrics

[aldy505]

Problem Statement

This is not necessarily "span metrics" per se, since this issue is for enabling the EAP (Event Analytics Platform) Spans feature, which right now holds the span metrics functionality. I don't know what this feature will hold in the future, but let's just see.

Product documentation: https://docs.sentry.io/product/explore/new-trace-explorer/ Product announcements: https://blog.sentry.io/find-and-fix-performance-bottlenecks-with-sentrys-trace-explorer/ Usage for JavaScript SDK users: https://github.com/getsentry/sentry-javascript/discussions/13136

Solution Brainstorm

The way we'll tell you how to configure this should be versioned (learned this the hard way from User Feedback feature). Grab the version you're currently on (or if yours is higher than any of these, choose the highest one).

• Setup Guide for 25.2.0
• Setup Guide for 25.3.0
• Setup Guide for 25.4.0
• Setup Guide for 25.5.0
• Setup Guide for 25.5.1