fix(instrumentation): Make SentryGenerateIntegrationListTask configuration-cache compatible

[romtsn]

📜 Description

The task inputs were not properly wired, so running with config-cache enabled resulted in inconsistent integrations list being written to the manifest + unnecessary task reruns. Using flatMap on the input + returning a Provider from SentryModulesService fixes the problem.

💡 Motivation and Context

Fixes #846

💚 How did you test it?

Manually + automated

📝 Checklist

• I reviewed the submitted code
• I added tests to verify the changes
• I updated the docs if needed
• No breaking changes

🔮 Next steps