Add test to verify transactions from sentry-native are sent to relay

[markushi]

📜 Description

#skip-changelog

As a follow-up to #4298

💡 Motivation and Context

💚 How did you test it?

📝 Checklist

• I added tests to verify the changes.
• No new PII added or SDK only sends newly added PII if sendDefaultPII is enabled.
• I updated the docs if needed.
• I updated the wizard if needed.
• Review from the native team if needed.
• No breaking change or entry added to the changelog.
• No breaking change for hybrid SDKs or communicated to hybrid SDKs.

🔮 Next steps

[github-actions]

Performance metrics 🚀

	Plain	With Sentry	Diff
Startup time	691.68 ms	795.75 ms	104.07 ms
Size	1.58 MiB	2.08 MiB	505.46 KiB

Previous results on branch: markushi/chore/integration-test-native-txn

Startup times

Revision	Plain	With Sentry	Diff
3953f2e	432.16 ms	491.44 ms	59.27 ms

App size

Revision	Plain	With Sentry	Diff
3953f2e	1.58 MiB	2.08 MiB	505.35 KiB

[JoshuaMoelans]

lgtm, thanks for adding this!