leverage Azure Pipelines to run Integration tests

[jlouros]

Use Azure Pipelines to:

1. spin-up a Docker container with Bitbucket installed https://hub.docker.com/r/atlassian/bitbucket-server/
2. create another container to execute integration tests

Between step 1) and 2) we need to properly configure Bitbucket. A major inconvenience is license lifetime, at the moment it expires every 3 months.

Associated PR: https://github.com/jlouros/StashApiCSharp/pull/56