Support Server-Timing Headers

### Problem Statement

RE: https://github.com/getsentry/sentry-javascript/discussions/5838#discussioncomment-5267299,

> Supporting https://developer.mozilla.org/en-US/docs/Web/API/PerformanceServerTiming seems very interesting, will ask our performance team to take a look!

This was discussed internally but it didn't move forward. This is a GitHub Issue feature request for supporting https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Server-Timing

### Solution Brainstorm

Show [Server-Timing headers](https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Server-Timing) data in Sentry spans