Action/Trigger event definition default retention intervals

[Bill Erickson]

Evergreen 3.0.

Bug #1672775 introduced "retention intervals" to action/trigger event definitions, allowing events and event data to be purged from the database after a configurable amount of time on a per-def level. As noted in the bug, there is little reason to keep data from many of the stock event definitions indefinitely. Some of them have a shorter lifespan than an ailing house fly.

I propose we set default intervals wherever it's reasonable to do so.

There are a few classes of data:

1. Single-use (print) data -- very short lifespan

These can likely be purged each day or thereabouts.

2. Email, print, phone notification data

Purging these is best for patron privacy. I equate these to the process of purging circulations and holds, though, and we don't apply default retention intervals for those, so it's not clear we should apply them here.

3. Other, e.g. EDI output, auto-lost events, etc.

We probably don't want any default retention intervals for these.

Thoughts appreciated.