customer docker spawner class

[Tianhao-Gu]

Copied directly from custom_spawner.py which will be deleted once docker spawner is setup.

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 16.66667% with 60 lines in your changes missing coverage. Please review.

Project coverage is 56.20%. Comparing base (6d8a032) to head (81cf6e0). Report is 4 commits behind head on main.

Files with missing lines	Patch %	Lines
src/jupyterhub_config/custom_docker_spawner.py	16.66%	60 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #93 +/- ## =========================================== - Coverage 68.37% 56.20% -12.17% =========================================== Files 5 6 +1 Lines 234 306 +72 =========================================== + Hits 160 172 +12 - Misses 74 134 +60 ```

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[MrCreosote]

To be clear I've already reviewed everything in the file here; the only change is the superclass?

[Tianhao-Gu]

To be clear I've already reviewed everything in the file here; the only change is the superclass?

yea. Directly copied and pasted from previous custom_spawner class.