Standardized code formatting for Robot tests

[albinsuresh]

Is your refactoring request related to a problem? Please describe.

Not having a standard formatting guideline for robot tests results in different developers applying different styles and sometimes results in a lot of unnecessary formatting changes in PRs like this one: https://github.com/thin-edge/thin-edge.io/pull/2510/files#diff-da492c97262815c2fb72d74969479a29491c0c654d5a626a9d01ce3d21d7df16

Describe the solution you'd like

Apply a standard formatter to the project using some tool like Robotidy and make sure that the recommended styling is adhered to in PRs as well, by adding this check to the PR workflow.