Add types for event.context

[philipphofmann]

Description

At the moment, the event.context is a dict of string:any, but we can add a statically typed data class to know contexts such as app, os, etc.

https://github.com/getsentry/sentry-cocoa/blob/8607e67a262a3e958b22e861bba7a57ec965b89c/Sources/Sentry/Public/SentryEvent.h#L128-L133

[github-actions[bot]]

This issue has gone three weeks without activity. In another week, I will close it.

But! If you comment or otherwise update it, I will reset the clock, and if you label it Status: Backlog or Status: In Progress, I will leave it alone ... forever!

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