Document `lastEventId` with User Feedback

[bruno-garcia]

The User Feedback docs for SDKs (other than React Native and PHP) we have no reference of lastEventId.

This is useful when using the API in the SDK as well as the crash report modal, on server side rendered pages.

• [x] https://github.com/getsentry/sentry-java/issues/3236
• [ ] Python: https://docs.sentry.io/platforms/python/user-feedback/
• [ ] Unity: https://docs.sentry.io/platforms/unity/user-feedback/
• [ ] Unreal: https://docs.sentry.io/platforms/unreal/user-feedback/
• [x] https://github.com/getsentry/sentry-dart/issues/1902
• [ ] https://github.com/getsentry/sentry-kotlin-multiplatform/issues/193
• [ ] https://github.com/getsentry/sentry-cocoa/issues/3691

Relates to:

• https://github.com/getsentry/sentry/issues/65728

[getsantry[bot]]

Routing to @getsentry/product-owners-user-feedback for triage ⏲️