### _Why are the changes needed?_
### _How was this patch tested?_
- [ ] Add some test cases that check the changes thoroughly including negative and positive cases if possible
- [ ] Add screenshots for manual tests if appropriate
- [ ] [Run test](https://kyuubi.apache.org/docs/latest/develop_tools/testing.html#running-tests) locally before make a pull request
Closes#3179 from zhaomin1423/custom_event_doc.
Closes#3179
9456c997 [Xiao Zhao] fix
2e6f3030 [Xiao Zhao] fix
c13bdb5b [Min] update
ff88386e [Min] fix
38a5708d [Min] Add custom event handler docs
Lead-authored-by: Min <zhaomin1423@163.com>
Co-authored-by: Xiao Zhao <zhaomin1423@163.com>
Signed-off-by: ulysses-you <ulyssesyou@apache.org>