investigate an option to use direct stf-api for internal communication

[vdelendik]

as of now we use STF_URL and token from variables.env. It uses external ip address and might route externally.

we can keep STF_URL as is but override among other envitonment variable for mcloud-grid only using:

     - STF_URL=http://stf-api:3000/

above update will guarantee routing internally inside the same docker network.

[vdelendik]

done. for testing it should be enough to do setup, generate and reuse STF_TOKEN. During mobile testing double check that devices are occupied by user in STF.

[dhreben]

Verified