Add check for HTML in product category web description to readiness wizard

Two customers have fallen foul of the update to block HTML in the product category description.

Once we update the plugins to output the specification field as well, it will be super-easy to resolve this problem via a script and a plugin change ... we just need to know to do this.

Therefore we should update the readiness wizard to give this as a warning and a recommendation.

I.e. if this field contains HTML for any product group then give a warning, and tell the customer/support to move this data to the specification field and to change the plugin configuration to output that field instead.