Add Search task stats in task cancellation monitoring service

[sgup432]

Is your feature request related to a problem? Please describe.
To address a comment from PR:
#7642

• For now, we are only keeping track of cancelled tasks which have been running more than > threshold seconds. We can also consider to keep track of all cancelled tasks.
• We also need to consider adding SearchTask as part of stats. As of now, we are only tracking SearchShardTask stats.

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