Ability to add 3bot packages in a subfolder of a github repo

[robvanmieghem]

Description

Currently it is only possible to add a package in the root of a github repo using the giturl parameter in the packagemanafer add method. using a giturl like git_url="https://github.com/threefoldfoundation/tft-stellar/tree/master/ThreeBotPackages/activation-service" would be nice since we can keep functionally related packages together in a single repo. Repo explosion makes things unclear and hard to mamage.

[ashraffouda]

should be solved after merging this #1394