Update UW http client

[mar235av]

For connections to external web resources, such as GWS, we use a custom http client built using Apache HttpClient version 4.5.

Shibboleth 5.X has updated to the 5.3 version of HttpClient, which introduced significant changes to the API. There is a migration guide to assist in migrating applications to the new HttpClient API.

It is uncertain if it is possible to keep our existing code and include both versions of the HttpClient library, but this seems undesirable. Therefore, I'm going to at least explore what it takes to upgrade our client to the 5.3 version.

[mar235av]

Resolving this issue. Further analysis of the migration guide indicates that version 4.5 and version 5.3 of HttpClient can co-exist, they have different package structures and are thus completely independent.
Given that, I copied in the 4.5 library versions into the build (via edit-webapp/WEB-INF/lib, the same place the plugins are located), rebuilt and deployed the war file, which resolves the issue.
We should rewrite our web client for multiple reasons including this, but this work can be deferred until later.