Hide buttons for disabled features

[achilleas-k]

Previously we had a gin@home fork and container image that was modified for on-premise deployments of GIN. The modifications disabled features and UI elements that require extra (micro)services that we run ourselves:

• Data search (gindex)
• Dataset publication (gin-doi)

Maintaining a fork with these changes is cumbersome. Instead we should hide the UI elements (e.g., the Request DOI button) when the service is not configured.