fix health monitor task

[codewithbear]

I discovered that HealthMonitoringTask is currently broken. While the periodic task is scheduled according to config, the logic fails to update the CurrentHealthStatus bean.

See example in the added test HealthMonitorTaskSpec.groovy

I found out that the subscriber to reactiveSequence is not getting triggered. It looks like in the onSubscribe we have to explicitly call request method so that HealthIndicators would emit HealthResults

If we fix the above problem with use of request we run into another problem. onComplete in the subscriber reports that the status is UP, even though some checks might be DOWN, and the web endpoints report DOWN. So it looks like incorrect behaviour.

This PR proposes a rewrite in a more clear way and fixing the above problems:

• first, collect all publishers in a List
• use Flux.collectList to subscribe to all publishers and collect all results in one list
• Then we can operate on the final result list in a simple way to check if any status is down and report that. Only if all statuses are up then we report UP

[CLAassistant]

All committers have signed the CLA.

[wetted]

This apparently fixes issues I am having getting a related test to pass on #9895