Add audit event log.

[EreMaijala]

Audit event log can be used to store information about events such as user logins. This is also a prerequisite for the upcoming online payment support that needs to store events about payments.

This implementation is not exhaustive, but I tried to cover the functionality that we've had most issues dealing with, logins being the single most prevalent one.

TODO:

• Update https://vufind.org/wiki/administration:command_line_utilities#util_category
• Update changelog when merging (types/args added to ILSAuthenticator::sendEmailLoginLink and newCatalogLogin signatures)

[demiankatz]

Thanks, @EreMaijala -- I ran out of time before I could fully review all of the files here, but I found a few significant issues on my initial review. I'll look through the rest once you've had a chance to respond to this first round! (There are only two files I haven't looked at, so I'm nearly done in any case).

[demiankatz]

See below for one more comment based on a review of your latest diffs. Also note that the open Auth Manager comment remains unresolved.

I still need to review a couple more files, but thanks for all the progress so far!

[demiankatz]

Thanks, @EreMaijala, I've finished reviewing everything -- see below for a few more comments. The one about enums is the biggest issue; I don't mean to hold things up over it, but it seems like a decision we should make thoughtfully to be sure we keep our future options as open as possible.

[demiankatz]

Thanks, @EreMaijala -- see below for more discussion of enums and a trivial suggestion.

[EreMaijala]

@demiankatz Your suggestion is reasonable. I changed the type/subtype getters to always return a string. If, for some reason, the caller would want the enum, it can use the enum's tryFrom itself.

[demiankatz]

Thanks, @EreMaijala!