Data Model: Add facilityState attribute to ProcessingFacility

[tangobravo62]

For the user as well as for planning and product access purposes it is important to know, whether a processing facility is operational or not. Therefore a new attribute facilityState shall be introduced for processing facilities as an enumeration with the following values:

• DISABLED: The processing facility must not be used. All requests concerning a facility in this state shall return the HTTP code 400 (Bad Request)
• STOPPED: The processing facility is temporarily halted. The facility is available for order planning, but no job steps shall be started, and requests for product ingestion or download shall return the HTTP code 503 (Temporarily Unavailable) immediately.
• STARTING: The processing facility is in the run-up process. The facility is available for order planning, job step starting may be initiated, but may time out, all other requests shall return the HTTP code 503 (Temporarily Unavailable) either immediately or after a reasonable time out period.
• RUNNING: The processing facility is fully available. All requests are allowed.
• STOPPING: The processing facility is in the process of being stopped. No new job steps shall be started, but running job steps are allowed to finish and can be queried. All other requests shall return the HTTP code 503 (Temporarily Unavailable) immediately.

Allowed state transitions are DISABLED <--> STOPPED --> STARTING --> RUNNING --> STOPPING --> STOPPED.

All HTTP error status values shall be accompanied by an explanatory error message including the facility status.

Justification: Processing facilities may be taken down for maintenance, and processing facilities may be defined before they actually become available in the Cloud. Introducing a facility state prevents failing requests to unavailable facilities and creates transparency for the user.

[tangobravo62]

Data model updated, Facility Manager, CLI and GUI updated to handle new attribute.

TODO: Update Production Planner to respect facility state; TBD how the status changes (STOPPED --> STARTING --> RUNNING and RUNNING --> STOPPING --> STOPPED) shall be monitored.

Assigned to @emelchinger for update of Production Planner.

[tangobravo62]

Processing facility status now taken into account by Production Planner. Open question of monitoring will be handled in greater context of logging and monitoring for prosEO.