Add option to not consider word boundaries when processing keyword filtering (#7975)

* Add option to not consider word boundaries when filtering phrases

* Add a few tests for keyword/phrase filtering

app/models/custom_filter.rb

@@ -8,6 +8,7 @@
 #  expires_at   :datetime
 #  phrase       :text             default(""), not null
 #  context      :string           default([]), not null, is an Array
+#  whole_word   :boolean          default(TRUE), not null
 #  irreversible :boolean          default(FALSE), not null
 #  created_at   :datetime         not null
 #  updated_at   :datetime         not null