Fixes #30394 - allow non-admins deal with untaxed filters

Prior this non-admin user would have to have assigned Role without
taxonomies (global role) to be able to manipulate filters.
This allows manipulating Filters to any User with Filter perms.

Filters with taxonomies mean they apply to taxonomy. But given they have
taxonomies relations, they are expected to be taxable in our permission
model. All taxable resources have to have the same taxonomies as Filter
have.

Some filters doesn't have taxonomies as their underlying resource
doesn't have taxonomies. That mean they were unable to be touched by
non-admins prior this patch.

This also drops current taxonomy relations in migration and force flip
the `Override` flag to false for Filter resource filters.

app/models/filter.rb

@@ -61,6 +61,10 @@ def ensure_taxonomies_not_escalated
 
   validate :same_resource_type_permissions, :not_empty_permissions, :allowed_taxonomies
 
+  def self.allows_taxonomy_filtering?(_taxonomy)
+    false
+  end
+
   def self.search_by_unlimited(key, operator, value)
     search_by_limited(key, operator, (value == 'true') ? 'false' : 'true')
   end

db/migrate/20210609093404_drop_override_taxonomies_from_filter.rb

@@ -0,0 +1,8 @@
+class DropOverrideTaxonomiesFromFilter < ActiveRecord::Migration[6.0]
+  def up
+    perms = Permission.where(name: %w[view_filters create_filters edit_filters destroy_filters])
+    filters = Filter.joins(:filterings).where(filterings: { permission_id: perms })
+    filters.update_all(override: false)
+    TaxableTaxonomy.where(taxable: filters).delete_all
+  end
+end