[Feature] Store user's Name value as Display Name value if received

[pb-amy]

Allow institutions to send us user's preferred name as an (optional) standard value. Can use displayName, urn:oid:2.16.840.1.113730.3.1.241 (https://commons.lbl.gov/display/IDMgmt/Attribute+Definitions#AttributeDefinitions-displayNamedisplayName)

If we receive it from the institution, save it as the user's Display Name in Pressbooks.

Requested by (for internal purposes only): https://pressbooks.zendesk.com/agent/tickets/3834 (Boise State) & https://pressbooks.zendesk.com/agent/tickets/6451 (UM System)

See: https://github.com/pressbooks/pressbooks-saml-sso/blob/dev/inc/class-saml.php#L445 this function will match the SAML attributes for the PB username.

[pb-amy]

Related to this issue directly, it would be nice if the Display Name could auto-populate the "Display name" field so that the the Greeting message on the upper top right hand corner shows the user's Name by default and not their ID. (See a screen recording of this example here: https://drive.google.com/file/d/1mAkQ-2qnF4yiapKBovmGK59LRkrbRe1H/view)

Idea from this ticket (for internal purposes only): https://pressbooks.zendesk.com/agent/tickets/6537 (KPU)

[tw77]

Further interest in this feature expressed by UCF just now during a quick call to discuss their SSO setup.