IdP metadata config docs

[Tom Scavo]

We've overhauled the IdP MetadataConfiguration [1] wiki page and most
of its child pages. New child pages have been added as well. In
particular, if you're new to the Shibboleth IdP, the (new)
MetadataManagementBestPractices [2] child page will be of interest.

For long-time users, I have a couple of questions:

1. Is anyone using (or has anyone ever used)
ResourceBackedMetadataProvider? If so, can you briefly describe your
use case? (There isn't much in the archives about this esoteric
metadata provider.)

2. Is anyone pulling metadata from a git server (such as GitHub)? If
so, can you briefly describe your use case?

Your answers to these questions will help me write better documentation.

Thanks,

Tom

[1] MetadataConfiguration https://wiki.shibboleth.net/confluence/x/8YAOAQ
[2] MetadataManagementBestPractices
https://wiki.shibboleth.net/confluence/x/JQXKAg
[3] ResourceBackedMetadataProvider
https://wiki.shibboleth.net/confluence/x/CAMnAQ