This PR adds the build, test & package workflow to the client code base as well.
In order for us to run the Cypress tests, we also spin up a local server in a Docker container and run all our tests against that server. This ensures that our tests are faster to run as well.
We also introduce the concept of stubbing network requests by stubbing the API that fetches the property pane configuration from the server.
Results for the Cypress tests can be viewed at: https://dashboard.cypress.io/projects/eyxvp8/runs/
