Limit execution time evaluating the health indicators

[ceremo]

The health actuator endpoint can become unresponsive if one of the health indicators gets stuck. This behavior affects the responsiveness of the health endpoint, causing it to be unresponsive until all health indicators are evaluated.

It could be beneficial to execute the health indicators asynchronously. For instance, in servlet applications, this can be achieved by evaluating the health indicator in a single-thread executor and a Future. In reactive applications, health indicators can be subscribed to using a single scheduler for the Mono created in each health indicator. In both cases, a timeout duration (property) can be established for evaluating each health indicator. In addition, it would be great if when a health indicator cannot be evaluated within the specified time, it reports an UNKNOWN status.

What's your opinion?

[snicoll]

This is a duplicate of #2652, #25459, and #4391 (comment)