Refactor the openshift-io Forge add-on to reuse services in the fabric8-launcher backend

[gastaldi]

As part of the unification efforts in the fabric8-launcher backend, the existing OSIO add-on must be refactored to reuse the services and the libraries we already provide in https://github.com/fabric8-launch/launcher-backend. This means that the OSIO add-on needs to be included as part of the launcher-backend repository

The launcher-backend provides services that interacts with OpenShift instances, Github and Keycloak (KeyCloak is used internally for querying access tokens).

This is a subtask of #1317

[gastaldi]

The OSIO addon will remain as is until the new UXD flow is implemented. Closing this issue now