Ember pageload and navigation spans lack span description inference attributes

[Lms24]

Description

Surfaced via #24168 (comment), Ember pageload (and likely also navigation) spans don't carry a name that's equal to any of the attributes we need to infer the span description: https://getsentry.github.io/sentry-conventions/descriptions/#browser-pageload

We have a couple of options:

1. router.navigation.route.id
2. theoretically, url.template but the current pattern in the test doesn't seem to actually be a url
3. we override this with sentry.description to avoid span description inference and define the description locally in the SDK.

[linear-code]

JS-3649