Feature Request: Add support for user policy banner or page

[hansen-m]

A useful feature to have would be a user policy page or pop-up that a user was required to read and accept before being allowed to continue on and use onDemand (or possibly per-cluster?).

Configuration ideas:

• Localizable policy text (customizable as plain, Markdown and/or HTML)
• Button text (if a decline/disagree button is included, then a URL to redirect to if clicked)
• Required "always" at each login or "once" per-user (with timestamp stored in ~/ondemand)
• Version changes (and an updated policy requires new accept)

A workaround to not having this feature is to use something like a public welcome page but not ideal: https://discourse.openondemand.org/t/public-welcome-page/1922

Discourse post: https://discourse.openondemand.org/t/add-policy-banner/3535