[K8S][HELM] Add command and args configuration support

[dnskr]

Why are the changes needed?

The change allows to change default command to launch Kyuubi and pass additional command line arguments.
It's needed if the chart user wants to print message, create files or similar in main container (kyuubi-server) when pod starts.

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 locally before make a pull request

[codecov-commenter]

Codecov Report

Merging #4606 (5e0ba5b) into master (cee2f00) will decrease coverage by 0.05%.
The diff coverage is n/a.

@@             Coverage Diff              @@
##             master    #4606      +/-   ##
============================================
- Coverage     53.32%   53.28%   -0.05%     
  Complexity       13       13              
============================================
  Files           577      577              
  Lines         31584    31584              
  Branches       4248     4248              
============================================
- Hits          16843    16830      -13     
- Misses        13154    13165      +11     
- Partials       1587     1589       +2     

see 8 files with indirect coverage changes

📣 We’re building smart automated test selection to slash your CI/CD build times. Learn more

[pan3793]

I'm not sure it's a good practice to allow user customize the start command, any examples?

[dnskr]

I'm not sure it's a good practice to allow user customize the start command, any examples?

I think it is not a good practice for production usage, but very helpful for investigation, development and workarounds.

For example

• Airflow allows to specify custom command and args airflow/chart/values.yaml#L455-L463. I used it to create task pools on startup and to install additional python packages without building custom docker image.
• Superset also has possibility to override command: superset/helm/superset/values.yaml#L254-L257
• One more use case [Bug] Executing kyuubi status returns 'Kyuubi is not running' in docker container #4515 (comment)

So it is not critical change, however gives more flexibility to the helm chart.

[pan3793]

Thanks @dnskr for listing usage examples, it makes sense then.