Remove all Docker containers after an Actions workflow

[kmazurek]

We need to make sure that a proper cleanup is performed after a test, regardless of how the test was closed. Currently, when a test is stopped forcefully it does not remove some of the Docker containers started as part of it (i.e. the ones which are started dynamically, for example provider and requestor nodes).

Solution proposed by @shadeofblue: include an Actions step which removes all containers before and after the tests step in a workflow.