Sanitize helper for Resource fields that may contain permitted HTML tags

For now, this just applies to the long_description field on Resource...

A helper method that sanitizes a given string such that only approved HTML tags are included is needed. The approved HTML elements as of now are:

• p
• a
• strong
• em
• br

And approved HTML attributes are:

• href

This helper method should be applied to selected attributes (currently only long_description) whenever they are saved - this includes during DOOR Import (so in the ProtoResource) and during normal CRUD in the UI.

https://api.rubyonrails.org/classes/ActionView/Helpers/SanitizeHelper.html#method-i-sanitize