HTTP Client Attributes

[Tom Scavo]

Okay, the "Attributes" sections on the following wiki pages have been
overhauled:

MetadataConfiguration https://wiki.shibboleth.net/confluence/x/8YAOAQ

DynamicHTTPMetadataProvider https://wiki.shibboleth.net/confluence/x/o4AgAQ

FileBackedHTTPMetadataProvider https://wiki.shibboleth.net/confluence/x/kQInAQ

I'm at a stopping point so now is a good time to review, comment
and/or edit. In particular, on the DynamicHTTPMetadataProvider page,
there's this: "For optimal performance, configure a custom HTTP client
that [performs HTTP conditional GET]." I don't know how to do that so
perhaps someone else can pencil that in.

Once the dust clears, I'll review the "Child Elements" sections on the
above pages. On the DynamicHTTPMetadataProvider (at least) that
section needs work.

Tom