* Removed using scheduler from action execution heartbeat checker
in favor of regular threads.
* Added the new config options "batch_size" under [action_heartbeat]
group to limit a number of action executions being processed during
one iteration the checker.
* Added a test checking that an action execution is automatically
failed by the heartbeat checker.
Closes-Bug: #1802065
Change-Id: I18c0c2c3159b9294c8af96c93c65a6edfc1de1a1
2d74e6ebac