API: Adding the storage service metrics definition
API: Adding the storage service metrics definition

This adds the storage service metrics that is based on the
StorageServiceMetrics class.
The following command where added:
get_metrics_load
get_exceptions
get_total_hints_in_progress
get_total_hints

Signed-off-by: Amnon Heiman <ed5fc74c4692051ad0b19749fd7cea6ec2d74b9e@cloudius-systems.com>

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