Independent test runs #272

Let's adjust the test runs to make them independent between runs. They currently share the same two test accounts, workspace and projects. This might be problematic when you want to run tests from multiple branches/jobs/matrix at once.

We should create a new user (and a new workspace) with each test run.
The logic can work in a way that if you do not pass the current environment variables, we register new user and use it for testing.
If you pass in the environment variables, we would use those (so it does not create a new user when running tests locally)

Please note that we need to set a correct plan type for the newly created workspace (API endpoint PATCH v1/tests/workspaces/{id})