There seem to be a lot of cases where the suffix of an action (e.g.
".html") is set to bogus data, such as "*/*" or entire URLs. This can
increase cardinality of our metrics, and isn't very useful for
monitoring and filtering. To work around this, we enforce a whitelist
containing a few suffixes we actually care about. Suffixes not supported
will be grouped under the action without a suffix. This means that a
request to "FooController#bar.jpeg" will be assigned to
"FooController#bar".