Support permissions for guides / manuals & Table of Contents

We should support documentation to be locked behind permissions, both on the overall guides / manuals as well as on the individual permissions.

This will make it a lot easier for developers to automatically scope the content that is presented to the end user because they can reuse the same permissions that any given functionality is locked behind in order to block access to the documentation for that functionality; thus ensuring that users without access to do a given action won't have to see the documentation for something they cannot themselves do. We can also make this system optional by way of a winter.docs.view_all permission that can bypass any permissions set on the documentation content if desired.

The issue does not name files or tests. Start by mapping the plugin entry points for guides, manuals, and the Table of Contents, then determine where documentation permissions and the optional winter.docs.view_all bypass should be defined. Done means access is restricted at both levels and the bypass behavior is covered.