Bootstrap AppEngine service

[palazzem]

Once the AlertingClient can be used programmatically as an isolated component, an AppEngine application must provide the following functionalities:

• Google sign-in to replace Elmo credentials
• AppEngine multi-tenant config to store Elmo credentials
• AppEngine service must use the AlertingClient to interact with the main Elmo service
• AppEngine service must receive Elmo credentials and use KMS to retrieve an encryption key to safely store these credentials in Google Cloud Storage
• Arm and disarm functionalities must be provided

[palazzem]

The approach has been changed and no credentials are stored in GCP. Elmo project is a stateless REST Adapter that receives REST calls, and translates these calls to the right Elmo command.

Considering Elmo a stateless service, it will be deployed as Google Cloud Function. Closing all related tasks.