Get JUPYTERHUB_API_TOKEN from secret

[NarekA]

Trying to reslove https://github.com/jupyterhub/kubespawner/issues/398

This might be redundant from https://github.com/jupyterhub/kubespawner/pull/471

[welcome[bot]]

Thanks for submitting your first pull request! You are awesome! :hugs:
If you haven't done so already, check out Jupyter's Code of Conduct. Also, please make sure you followed the pull request template, as this will help us review your contribution more quickly. You can meet the other Jovyans by joining our Discourse forum. There is also a intro thread there where you can stop by and say Hi! :wave:
Welcome to the Jupyter community! :tada:

[sstarcher]

@NarekA @dolfinus any engagement on this? Anyone else able to review?