Publish prereleases automatically

[jasongrout]

In #172, we publish a prerelease manually. It would be great if we could update that branch every time we had a prerelease (like every week or two). We could rever, or our own instance of the autotick bot, or just our own custom workflow in the release process.

Code for the bot is at https://github.com/regro/cf-scripts and it looks like https://github.com/regro/cf-scripts/blob/master/conda_forge_tick/migrators/version.py might a relevant file.

[bollwyvl]

#267 might have helped, let's monitor this...

[krassowski]

@bollwyvl what would be needed to publish 3.6.0beta? Would it go to jupyterlab_alpha as in #273?

[bollwyvl]

I think we're good: #355