Add GCPInstanceService which used to monitor and suspend gcp instances if instance not used for a while.

[ekharkunov]

• Added new service that implements VM state management.
• Add new endpoint to set maintenance mode (update last used timestamp to prevent VMs from suspending/resuming VMs if it was suspended)

General implementation:

• At startup service look over extender.service.remote-builder.platforms and form maps with instance name and update last "touched" timestamp
• According to last "touched" timestamp and configured extender.gcp.controller.time-before-suspend service checks every extender.gcp.controller.check-period do VM need to be suspended.
• Before every request to remote builder we invoke GCPInstanceService.touchInstance to update last "touched" timestamp

Example of configuration:

extender:
    gcp:
        controller:
            enabled: true
            project_id: ${project_id}
            zone: ${vm_zone}
            wait-timeout: 60000
            retry-attempts: 3
            retry-timeout: 10000
            time-before-suspend: 1800000
            wait-startup-time: 10000
            check-period: 60000
            gax-max-thread-count: 10