Automate deployments via github actions/apps

[thermokarst]

Improvement Description
Right now deployments of q2view require a manual building step, and then pushing up one or more commit to https://github.com/qiime2/view.qiime2.org. It would be neat to automate this, perhaps when new commits to the master branch on this repo are created, a GitHub Action could build the source, then open a PR up on the https://github.com/qiime2/view.qiime2.org repo, for our review. Maybe that last part isn't necessary, though - let's discuss.

[gregcaporaso]

Related to #128.