Write smoke testing ADR

[jisantuc]

Per the application setup ADR,

• Continuous integration checks passing on a PR must mean that the branch is safe to deploy. This will require more care around migrations than usual and a more thorough exercise of the application in tests than we have in Raster Foundry. As long as this repository is just an API, that probably means generative testing of workflows modeled through API interaction both for correctness and performance regressions. I believe that we already have the tools and expertise on the team to do this.
• The application should also include smoke tests. Smoke tests will be a new feature of CI for us. We should be able to rely on the small application scope to ensure that we can define a reasonable standard for "not on fire."

We have a pretty good sense of how to do the first part (scalacheck + http4s testing, woohoo). We don't have a good idea of how to do the second one. Figure out how to run smoke tests in CI, and write an ADR about it.