Make reporting pre-warmed app starts GA

[philipphofmann]

Description

With #1969, the SDK reports pre-warmed app starts when enabling the experimental feature enablePreWarmedAppStartTracking.

getsentry/sentry-docs#5762 points the feature out in the docs. After validating this feature with some customer data we must decide if we can make it GA by also adding a dashboard so users see the difference between different app start types in Sentry, or if we drop the feature cause it's not working properly.

We should also document the app start type in the search properties list.
Also, having this field in the UI helps with the discoverability of the searchable field, similar to this.

Also related to #1897.

[philipphofmann]

Was fixed with #3536.