Previously, if an HTTP request that used a templated URI was handled
by something other than Spring MVC, a potentially unbounded number of
metrics would be created. This happened because, in the absence of
Spring MVC's best matching pattern attribute, MetricsFilter would fall
back to using the request's path. If the handling route was templated,
MetricsFilter would be unaware and would record different metrics for
each different path, rather than a single metric for the matching
pattern.
This cimmit updates MetricsFilter so that it falls back to using
unmapped when Spring MVC's best matching pattern attribute is not
available. This ensures that an unbounded number of metrics will no
longer be created, at the cost of losing specific metrics for requests
that are not handled by Spring MVC and that do not use a templated
path.
Closes gh-5875