MAINT - Bump nodejs version

[trallard]

Closes #323

Description

I am unsure why we were pinning to 16.x on nodejs in multiple places (there was no engine entry in the package.json, and I have been building/testing this project with node 20 with no problems.

This pull request:

• Bumps node version in GitHub workflows
• Bumps base node Docker image
• Bumps node version in dev_environment.yml
• Rename conda env (give a more descriptive name)
• Document use of conda env in README (related to DOC - environment-dev.yaml file for setting up dev env #338 - though this needs documenting in the conda-store-ui docs too)

Pull request checklist

• Did you test this change locally?
• Did you update the documentation (if required)?
• Did you add/update relevant tests for this change (if required)?

Additional information

[dcmcand]

Thanks for this @trallard! 🚀