Start/stop integration test server on-demand

[Andy-Grigg]

Closes #48

This PR enables the following functionality:

• Start the integration test server
• Check that the server is healthy before starting integration tests
• Stop the server when the workflow is finished
• Stop the server if the workflow is cancelled or if a job fails
• Don't do anything with the server if we aren't running integration tests (e.g. dependabot)
• Don't stop the server if it wasn't started by this workflow

The final task isn't possible because the principal doesn't currently have permissions to inspect the status of the VM.

However, I have put the foundations in place to enable this by checking if the conclusion of the start_vm job was anything other than skipped. The idea being that in future we can add a job that checks the status (e.g. get_vm_status), and then have the start_vm job proceed only if the result of the get_vm_status job is something like 'stopped' or 'deallocated'.

[da1910]

One comment about logging, otherwise looks good and seems to work just fine!