Add RELEASE.md, and update release workflow to use PyPI's trusted publisher

[Sheila-nk]

• added RELEASE.md file
• updated PyPI permissions in release.yaml file
• removed jupyterhub-bot as a maintaniner on PyPI
• added repo's release.yaml as a trusted publisher on PyPI
• deleted GitHub Secret pypi_password

Closes #58

[Sheila-nk]

I also created a release environment in this repository that the workflow will use for publishing. I am not too sure it is necessary since I have not set any protection rules or environment secrets which would be necessary if the repo had maintainers without publishing access, which is currently not the case.

Let me know if this is a standard thing in the organization. Otherwise, I will need to delete the environment and edit the trusted publishers in PyPI to remove the environment name.

Here is the publishing information page:
https://pypi.org/manage/project/pytest-jupyterhub/settings/publishing/

[consideRatio]

Nice this LGTM!

I pushed a commit adding this to the changelog so that is done as well, and with that, I think finally we can go for the release!!

If the added commit is okay with you, go for a merge -> release!

[Sheila-nk]

Thanks for opening an issue on this and for reviewing this PR @consideRatio ❤️
Merging this PR now and moving on to releasing this package 🚀