Build conda pkgs with conda-forge

[willfurnass]

Proposed change

It would be useful if batchspawner could be installed from the conda-forge conda channel.

Alternative options

People can pull batchspawner conda packages from https://anaconda.org/hcc/batchspawner but a 'JupyterHub' ecosystem-branded package would be more reassuring.

Who would use this feature?

Anyone wanting to install batchspawner using conda.

(Optional): Suggest a solution

Copy and adapt the conda-forge feedstocks used for other JupyterHub Spawner implementations - see https://github.com/conda-forge?q=jupyterhub&type=&language=&sort=

[ericdwang]

Looks like version 1.1.0 was added to conda-forge 6 months ago and version 1.2.0 the day after the PyPI release: https://anaconda.org/conda-forge/batchspawner/files