TiKV RawKV Mode: API v2 TTL Limitation, Titan Usage, and Lack of TiCDC Support

## Feature Request

**Is your feature request related to a problem? Please describe:**
We are running a TiDB cluster on Kubernetes in TiKV RawKV mode with TiDB disabled in the TidbCluster manifest. While evaluating performance improvements, we considered using Titan (RocksDB plugin), which is documented to enhance read/write performance. However, with the introduction of API versions (v1 and v2), we are facing limitations—API v2 lacks TTL support, which is required for our use case, forcing us to stay on API v1. Additionally, TiCDC does not support RawKV mode, preventing us from using change data capture, which is important for our architecture.

**Describe the feature you'd like:**
We would like support for TTL in API v2 so that we can adopt it without losing required functionality. Additionally, we would like clarity and best practices around using Titan in RawKV mode alongside API version constraints. We also request support for TiCDC (or equivalent CDC functionality) in RawKV mode.

**Describe alternatives you've considered:**
We have considered continuing with API v1 to retain TTL support, but this limits our ability to adopt newer improvements in API v2. For CDC, we explored alternative approaches such as application-level change tracking or external streaming solutions, but these add complexity and operational overhead compared to native TiCDC support.

**Teachability, Documentation, Adoption, Migration Strategy:**
Clear documentation and guidance on API version selection, Titan usage in RawKV mode, and feature compatibility (TTL, CDC, etc.) would greatly help adoption. If TTL support is planned for API v2, a migration guide from v1 to v2 would be valuable. Similarly, documentation or tooling for enabling CDC-like workflows in RawKV mode would improve usability and reduce the need for custom implementations.