CI: Add test stage to CI to submit tests to lava

Stage contains jobs to trigger tests on the lava server. It currently also deploys the artifacts in a way that they are available to local download and installation using the FNG_INSTALL variable for the lava devices.

There are jobs to trigger platform tests which are run once per given platform and smoke tests which run on all devices of a devicetype found.

The tests results are downloaded as junit and yaml and gitlab is configured to show the results of the subtests inside the MR.

The main functionality is done in submit_test.py which is part of the .gitlab-ci submodule, which is also pulled in this commit.