Multi DSN per Java Application support

### Problem Statement

I have a use case where I'd like to separate Projects by team with multiple DSNs in a single JVM application. I tried local testing of a workaround solution (https://github.com/getsentry/sentry-java/compare/feat/multi-dsn-playground) with custom ITransportFactory and EventProcessor which seemed to work. The only issue was that `RequestDetailsResolver` was package-private in the SDK, so my application didn't have access and I had to rewrite my own RequestDetailsResolver, DSN classes. `+ SentryClient.SENTRY_PROTOCOL_VERSION` within the RequestDetailsResolver was also unaccessible, so I have to hardcode the protocol version.

### Solution Brainstorm

Is it possible to make this class public?
https://github.com/getsentry/sentry-java/blob/main/sentry/src/main/java/io/sentry/RequestDetailsResolver.java#L10

從 sentry/src/main/java/io/sentry/RequestDetailsResolver.java 和連結的 multi-dsn-playground 比較開始。檢查自訂 ITransportFactory 和 EventProcessor 如何使用 RequestDetailsResolver，包括 SentryClient.SENTRY_PROTOCOL_VERSION，並查看留言串以了解預期的公開 API。完成的標準是：multi-DSN 使用情境不再需要複製的 resolver 或 DSN 類別，並且有適當的 SDK 測試涵蓋。

由索引模型根據 Issue 內容生成。