improvement: standard development docker image

[kyleburton]

Having python, pyenv and other tooling raises the effort of getting started for developing on inline-plz. In order to streamline the effort of getting set up for development, and to reduce inconsistencies between developer environments, we could introduce a standard development Docker image as well as some command line shims or helpers for executing build tasks (running tests, performing the dry-run, etc). This sould reduce dependencies for working on the project to: git, docker and bash.