Document Prometheus registry onMeterRegistrationFailed callback

[shakuzen]

This is exactly what happened. I'm an app using micrometer + some custom registry to micrometer + prometheus.
I spent a few hours trying to figure out why some metrics don't appear after adding prometheus.
I think it would be better to make this behaviour configurable.

Originally posted by @angry-cellophane in #2400 (comment)

[shakuzen]

First, sorry for the frustration and time spent due to the current behavior, @angry-cellophane. We need to do a better job documenting this, so I've made this issue to track that.

I think it would be better to make this behaviour configurable.

For what it's worth, the behavior is configurable. You can restore the previous behavior of an exception being thrown and an error logged with the throwExceptionOnRegistrationFailure method on the PrometheusMeterRegistry.

[izeye]

I created #4878 to try to resolve this.

[shakuzen]

Thanks so much, @izeye.
Closed by #4878