Checks integration in AzureDevOps

[applejag]

Add checks, or "statuses" as they're called in the Azure DevOps API. This implicitly makes a pull request not mergeable until the status is "succeeded"

API docs: https://docs.microsoft.com/en-us/rest/api/azure/devops/git/statuses/create?view=azure-devops-server-rest-5.0

On the commit:

In commit list:

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We want to add this throughout the provider repos. So it would behoove us to figure out a way to do this in a generic manner.
Old thought was to use rabbitmq events, but that's no longer an obvious solution as it does in fact induce a lot of overhead for users trying to install Wharf. Would be better to just let the API talk with the providers directly.

Suggest writing an RFC on this: https://github.com/iver-wharf/rfcs