Add events for On Demand Certificates

[oliverdunk]

In my blog post here, I explain how I added two new events to Caddy:

• OnDemandCertObtainedEvent
• OnDemandCertFailureEvent

I'm opening this issue to ask if this is something that is worth PRing to introduce upstream? It seems like a minor change, and I can't see any downsides, but I wasn't sure if there was a reason for these not existing already.

[francislavoie]

Nothing to lose by making a PR. Go for it!

Events are relatively new and it's really dependent on what kind of features plugin authors would like to implement. Your use-case definitely seems valid, so I don't see why it wouldn't get merged.

[mholt]

Implemented in #4984