UI test for "Hide search bar" setting

[individual-it]

a test is needed for #3817
the main challenge here will be to edit the config json file from the test step, and maybe a reload of phoenix is needed alsoe

alternatively we can have two separate tests for OCIS & for oC10, with separate config json files as input

[kulmann]

Just tested with page reload. In case you start ocis with PHOENIX_WEB_CONFIG=/path/to/config.json ./bin/ocis server it actually works without ocis restart to edit the config + see the change after a browser reload.