Support for Azure Boards

I was recently approached by a colleague who suggested we might want to add support for [Azure Boards](https://azure.microsoft.com/en-us/services/devops/boards/), given that it has currently more than 1.2M monthly users. It is an interesting proposition and could serve as a proof that the integration can be more generic and support multiple platforms. One caveat is that we would have to, once again, rename the repository :-)

There are currently still a few outstanding items we should address for the JIRA integration, but if we can gather customer / prospect interest, then this might be an interesting project.

No files, tests, or entry points are named. Start by reviewing the existing JIRA integration and its outstanding items, then define the Azure Boards scope, platform-agnostic changes, and acceptance criteria before implementation; the issue currently does not specify what completion looks like.

Written by the indexing model from the issue text.