ci: introduce circleci workflows

[Jusshersmith]

Problem

There is currently no automation around tagging SSO docker images with the latest tag.

Solution

This PR proposes moving our CircleCI config to use the ‘workflows’ method introduced in CircleCI 2.0, allowing us to better separate and orchestrate individual jobs.

• Separates circleci jobs into logical ‘workflows’:

  • build
  • push-sso-dev-commit (only runs if build succeeded, and on each commit)
  • push-sso-dev-latest (only runs if build succeeeded, and only on master branch)
  • upload-codecov (only runs if build succeeded)

• Makefile tasks:

  • new imagepush-latest task (pushes with the latest tag)
  • changes imagepush to imagepush-commit to help separations for circleci
  • adds the latest tag to the image in the releasepush task.

Notes

• We could also separate the build and test steps.
• We can solve the problem statement without also moving to the workflows method, but this seemed like a logical advancement

Relevant issues: #193

[Jusshersmith]

I’m not entirely sure why ci/circleci Expected — Waiting for status to be reported still shows at the moment 🤔

[jphines]

Let's get this merged once we understand why the ci/circleci isn't working.

[Jusshersmith]

Why ci/circleci wasn’t working: https://circleci.com/docs/2.0/workflows-waiting-status/