[Task] Add user help documentation for Redis Sentinel and Apache Kvrocks monitoring

### Description

In HertzBeat, both **Redis Sentinel** (`app-redis_sentinel.yml`) and **Apache Kvrocks** (`app-kvrocks.yml`) are fully supported monitoring templates under the `cache` category with designated `helpLink` URLs:
- `https://hertzbeat.apache.org/docs/help/redis_sentinel`
- `https://hertzbeat.apache.org/docs/help/kvrocks`

However, the corresponding user help documents in `home/docs/help/` (English) and `home/i18n/zh-cn/docusaurus-plugin-content-docs/current/help/` (Chinese) are currently missing, and they are not included in `home/sidebars.json`. When users click the "Help" button from the HertzBeat console, it leads to 404 pages.

### Task List

- [x] Add English help doc for Redis Sentinel (`home/docs/help/redis_sentinel.md`)
- [x] Add Chinese help doc for Redis Sentinel (`home/i18n/zh-cn/docusaurus-plugin-content-docs/current/help/redis_sentinel.md`)
- [x] Add English help doc for Apache Kvrocks (`home/docs/help/kvrocks.md`)
- [x] Add Chinese help doc for Apache Kvrocks (`home/i18n/zh-cn/docusaurus-plugin-content-docs/current/help/kvrocks.md`)
- [x] Register both docs in `home/sidebars.json` under the `cache` category

Start by reading app-redis_sentinel.yml and app-kvrocks.yml to understand the monitored templates and their helpLink URLs. Add the English and Chinese documents at the four listed paths, register both entries in home/sidebars.json under cache, and verify the console Help links no longer lead to 404 pages.

Written by the indexing model from the issue text.