[ML] Failure persisting datafeed timing stats leaves datafeed in limbo

[droberts195]

Since 7.4.0 when a datafeed is stopped it tries to persist datafeed timing stats. However, this is done in the finally block in DatafeedManager.stop(), and if it fails for some reason then the datafeed is not fully stopped. It remains permanently in the stopping state, and due to #48931 there is currently no way to stop a datafeed that is stuck in the stopping state.

Failure to persist datafeed timing stats for some reason should be logged as a warning but should not prevent more critical datafeed shutdown actions from being attempted.

[elasticmachine]

Pinging @elastic/ml-core (:ml)

[przemekwitek]

This issue is now fixed in 7.5.0.