Package form disclaimer should be configurable

[jqnatividad]

Right now, you can explicitly specify a license.

In addition, there's a default Open Database License disclaimer for the metadata on the package_form snippet.

https://github.com/ckan/ckan/blob/8eec3e27c320baf29e0d99b2ce20ed14ae10b0d3/ckan/templates/package/snippets/package_form.html#L26

There was an extensive discussion on the reasoning behind this - ckan/ckan#1503, which holds true in the traditional "open data" use case, which does not apply to an enterprise DMS use case.

Why not make it a configurable option with the default value set to the existing text?

I realize that you can always override the snippet, but it'd be better if its easily configurable.