Add metrics: oldest_data_state and num_clones_older_than 1, 7, and 30 days

Added metrics for:

• data state: oldest_data_state (+ alarm, warning - if there is a oldest data state of more than 30 days.)
• clones: older_than_1_day
• clones: older_than_7_days (+ alarm, warning - if clones older than 7 days are detected.)
• clones: older_than_30_days (+ alarm, critical - if clones older than 30 days are detected.)

issue: #1 (closed)

The default alarm value can be overridden in the configuration file /etc/netdata/health.d/DLE.conf