Document "Requesting Admin Usage"

[GCHQDeveloper314]

For the Federated Store and other parts of Gaffer, there is an option in the code for userRequestingAdminUsage.

It appears this is so that an "admin" user with auths set in gaffer.store.admin.auth is able to perform operations which would otherwise require different auths. This is not documented in the old docs at all.

Exactly what this does and how it can be used should be investigated. These details should be included in a suitable part of the documentation - probably the administration guide.