feat: Add maxCacheItems

[philipphofmann]

📜 Description

Add maxCacheItems to SentryOptions to make the number of maximum envelopes
to keep in the cache configurable.

💡 Motivation and Context

Fixes GH-899

💚 How did you test it?

Unit tests.

📝 Checklist

• I reviewed the submitted code
• I added tests to verify the changes
• I updated the CHANGELOG if needed
• I updated the docs if needed
• Review from the native team if needed
• No breaking changes

🔮 Next steps

[bruno-garcia]

LGTM but I raised a discussion about the value. 30's been our standard so far but since it had in-memory storage in mind, maybe we reconsider?

[philipphofmann]

LGTM but I raised a discussion about the value. 30's been our standard so far but since it had in-memory storage in mind, maybe we reconsider?

@bruno-garcia I'm also fine with increasing this, but it should be consistent across SDKs. Currently, we have 30 on Android and .NET.