feat(metrics): Add BeforeEmitMetrics callback #7984

Job	Run time
Swift Lint	19s
pod lint Sentry/HybridSDK	2m 4s
pod lint Sentry dynamic ios	2m 48s
Xcode Analyze	3m 36s
pod lint Sentry static ios	4m 17s
pod lint Sentry dynamic macos	3m 19s
pod lint Sentry static macos	3m 22s
pod lint Sentry dynamic tvos	3m 47s
pod lint Sentry static tvos	3m 17s
pod lint Sentry dynamic watchos	4m 7s
pod lint Sentry static watchos	3m 31s
pod lint SentrySwiftUI dynamic ios	2m 7s
pod lint SentrySwiftUI static ios	2m 11s
pod lint SentrySwiftUI dynamic macos	1m 50s
pod lint SentrySwiftUI static macos	2m 2s
pod lint SentrySwiftUI dynamic tvos	1m 26s
pod lint SentrySwiftUI static tvos	1m 40s
pod lint SentrySwiftUI dynamic watchos	1m 41s
pod lint SentrySwiftUI static watchos	2m 11s
	49m 35s

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