feat: added support for Azure DevOps output

[milanmayr]

What

Azure DevOps output can be set with the -o azuredevops flag

• docs have been updated
• tests have been added, and all are passing
• output follows formatting standards outlined in Azure DevOps' Logging commands > Formatting commands documentation

Why

To address #852

Usage example

$ conftest test -o azuredevops -p examples/kubernetes/policy examples/kubernetes/deployment.yaml
##[section]Testing 'examples/kubernetes/deployment.yaml' against 5 policies in namespace 'main'
##[group]See conftest results
##vso[task.logissue type=error] file=examples/kubernetes/deployment.yaml --> Containers must not run as root in Deployment hello-kubernetes
##vso[task.logissue type=error] file=examples/kubernetes/deployment.yaml --> Deployment hello-kubernetes must provide app/release labels for pod selectors
##vso[task.logissue type=error] file=examples/kubernetes/deployment.yaml --> hello-kubernetes must include Kubernetes recommended labels: https://kubernetes.io/docs/concepts/overview/working-with-objects/common-labels/#labels
##vso[task.logissue type=error] file=examples/kubernetes/deployment.yaml --> Found deployment hello-kubernetes but deployments are not allowed
success file=examples/kubernetes/deployment.yaml 1
##[endgroup]
5 tests, 1 passed, 0 warnings, 4 failures, 0 exceptions

Example

[jalseth]

LGTM, thanks for the contribution!