Consider adding a terminal error type that doesn't get retried

[alvaroaleman]

There are various cases in which a reconciler hits an error that it knows won't get resolved with retrying. Today, the common approach for this is to not return an error at all but just log this instead.

We should consider adding such an error type because:

• This is something that is frequently-ish needed
• Not returning an error means that terminal errors don't appear in metrics or the logs controller-runtime emits

[sbueringer]

Sounds reasonable to me

[TomNeyland]

There is some relevant discussion in #617