### _Why are the changes needed?_
Build the content for extension points documentation, pre-work for #3100
<img width="1767" alt="image" src="https://user-images.githubusercontent.com/8326978/179930987-1accbbb7-e804-4230-871f-6c4b1152f4a1.png">
1. the extensions are divided into 2: server side and engine side extensions. (Do we have client side extension support?)
2. the server side authentication page is cross-referenced by the security section, see 1 in the picture.
3. the engine side ones are grouped by different compute frameworks.
4. connector is one type of extension, so we cross-reference the connector pages directly, see 2 & 3 in the picture.
### _How was this patch tested?_
- [ ] Add some test cases that check the changes thoroughly including negative and positive cases if possible
- [x] Add screenshots for manual tests if appropriate
- [x] [Run test](https://kyuubi.apache.org/docs/latest/develop_tools/testing.html#running-tests) locally before make a pull request
Closes#3103 from yaooqinn/3101.
Closes#3101
a9ae3e32 [Kent Yao] [KYUUBI #3101] [Subtask][#3100] Build content for extension points documentation
3b7367e9 [Kent Yao] [KYUUBI #3101] [Subtask][#3100] Build content for extension points documentation
b5eda13e [Kent Yao] [KYUUBI #3101] [Subtask][#3100] Build content for extension points documentation
Authored-by: Kent Yao <yao@apache.org>
Signed-off-by: Kent Yao <yao@apache.org>
6c8024c8a4
