[FEATURE] Allow to turn off header link generation

[AronNovak]

Overview of feature request

Implement a feature in Islandora to allow or disallow generating links in the HTTP headers via a configuration setting.

What kind of user is the feature intended for?

This feature is intended for Developers and Systems Administrators who need control over the HTTP headers being sent from their Islandora instance.

What inspired the request?

Our hosting provider disallow too large response headers.
See https://docs.pantheon.io/guides/errors-and-server-responses/5xx-errors#503-header-overflow

What existing behavior do you want changed?

Currently, Islandora always generates links in the HTTP headers without an option to disable this functionality. This request seeks to add a configuration option to control this behavior.

Any brand new behavior do you want to add to Islandora?

Yes, a new configuration setting called allow_header_links should be added to Islandora's settings. This setting, when disabled, should prevent the generation of links in the HTTP headers.