CI using GitHub Actions

[ddohler]

Overview

travis-ci.org shut down, and migrating to GitHub Actions seemed easy and is our preferred solution anyway, so this makes the switch.

Notes

~This is draft while I test (I suspect CI may fail initially because I had problems with credentials locally).~

• The Esri credentials we had for omgeo testing seemed to have disappeared, so I created some new ones and updated the ones we have
• This is heavily cribbed from the setup for django-ecsmanage.

Testing instructions

• Push a dummy commit to this branch and confirm that it triggers a build (and that the build succeeds).
• I'm not sure whether we can fully test the release flow until this is merged to develop, but I believe the path to test should be as follows:
  • Register on TestPyPi and get account credentials (this is probably best done by someone with easy access to the email we use for company-wide accounts).
  • Put the account credentials into the appropriate secrets for this repository
  • Push a dummy tag and confirm that a release is made to TestPyPi
  • Confirm you can install the new release from TestPyPi

Assuming the above is completed, the following cleanup tasks also need to be done before merging:

• [x] Update the repository secrets to point to production PyPi
• [x] Remove the Delete me! commit from this branch / develop
• [x] Delete the test tag

[ddohler]

@azavea/operations -- I attempted to assign this to you, but it doesn't appear that GitHub supports assigning to or requesting review from teams, so I'm leaving this comment here; hopefully that's the appropriate path. Please review when you have a chance, thanks!

[colekettler]

Also, I think I figured out why you couldn't tag the operations team. It seems like you can only assign teams as reviewers in private repositories for the organization. I'm not totally clear on if that's due to team secrecy settings somewhere or if that's the intended default behavior.

[ddohler]

As I was rebasing to finish this, I discovered that matrix testing seems to cause the US Census geocoder to become unstable in some way that makes it unlikely that all three version tests succeed on any given run. A single Python version has a much higher chance of success, so rather than disable the US Census tests, I opted to reduce the testing matrix down to just Python 3.8. My reasoning is that this is an old library that doesn't do anything fancy syntax-wise, so the primary thing we need to be concerned about with testing different versions is probably the possibility of older constructs being deprecated in newer Python versions, so it made sense to focus on the newest version available. I also opened an issue to see if we can figure out a way to still run a multiple-version test successfully. https://github.com/azavea/python-omgeo/issues/66