User Feedback envelope

[armcknight]

Description

Package up the inputs from the form into the envelope format for transmission to the Sentry backend

[armcknight]

One thing to consider here is that we already have a method today to gather feedback: SentrySDK.captureUserFeedback We should keep that method for convenience and backwards compatibility.

However, SentryUserFeedback.eventId is currently a required property, which we want to move to becoming optional. That is public API, so changing it should be considered a major revision as anyone using it may encounter build breakages, if they are reading the property in Swift code, as it will become optional.