ADR-002: Taskfile for development automation

Every recurring developer workflow is a task in Taskfile.yml: the local Bitbucket stack, code and docs generation, the gates, the test suites, the docs site and the release checks. CI and the git hooks run the same tasks, so a check means the same thing wherever it runs. Use an existing task rather than running its commands by hand, and add a recurring workflow as a task with a clear name and description.

Task lists what exists (task on its own prints the list), runs on every platform bb is developed on, and composes tasks from other tasks.

Not chosen

• Shell scripts alone: Harder to discover, to compose and to keep consistent across contributors.
• A Makefile: Task's YAML is clearer to read, and composing workflows in it is simpler.