Updates the "Related articles" sections after the revisions to the
channel permissions documentation, focusing on the articles in the
"Channel management" section of the help center.
Renames file and redirects existing links to "help/user-roles" as
the previous content tracks to that current file's content.
Updates existing links (excluding ReadtheDocs) to go to either
"help/user-roles" or "help/manage-permissions" depending on which
help center article applies to the content.
