### _Why are the changes needed?_
`build/mvn` is slow than `grep`, the change is aim to simplify and speed up the project version evaluation in `docs/conf.py`
### _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
- [x] [Run test](https://kyuubi.readthedocs.io/en/master/develop_tools/testing.html#running-tests) locally before make a pull request
```
(apache-kyuubi) ➜ docs git:(doc-beeline) ✗ python
Python 3.8.12 (default, Sep 17 2021, 20:21:14)
[Clang 12.0.0 (clang-1200.0.32.29)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> import subprocess
>>> subprocess.getoutput("grep 'kyuubi-parent' -C1 ../pom.xml | grep '<version>' | awk -F '[<>]' '{print $3}'")
'1.8.0-SNAPSHOT'
>>>
```
Closes#4599 from pan3793/doc-version.
Closes#4599
7458aef5b [Cheng Pan] [DOCS] Simplify project version calculation
Authored-by: Cheng Pan <chengpan@apache.org>
Signed-off-by: Cheng Pan <chengpan@apache.org>
5e541fa09f