feat(automation): externalize grpc clients configuration

See merge request teraflow-h2020/controller!40

First working version of Device with Emulated and OpenConfig drivers (except device monitoring)

See merge request teraflow-h2020/controller!38

Deactivated some Device monitoring functionality partially implemented to enable a functional commit into develop.

Device:
- Implemented Driver API with some special resources to enable retrieving endpoints from devices, interfaces, and network instances.
- Implemented special resource_keys (_connect/*) to enable AddDevice to obtain settings used to connect to remote devices (address, port, username, password, etc.)
- Implemented Emulated Driver (only for testing)
- Implemented OpenConfig Driver (missing to implement monitoring; templates for Infinera devices to be tested with other device vendors)
- Minor bugs and code improvements
- Improved test unit to enable easy testing of vendor devices and keep credentials secret.

Integrated L3 services UPM

See merge request teraflow-h2020/controller!29

# Conflicts resolved:
#   .gitlab-ci.yml

Renaming the monitoring yaml file to follow the pattern expected by the  script.

See merge request teraflow-h2020/controller!37

feat: implementation of Policy service

See merge request teraflow-h2020/controller!36