Fix #1457 by adding context.MatchedRoute() method

[lammel]

This PR fixes issue #1457 by adding a MatchedRoute method to context that will only return the path of a registered route.
This will allow for easier identification of matched routes and metric providers to return a limited set of known routes.

The method is based on code that we used as a helper method to filter known paths for providing metrics of requested URIs.

Tests have been added.

[codecov]

Codecov Report

Merging #1502 into master will increase coverage by 0.08%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master    #1502      +/-   ##
==========================================
+ Coverage   84.38%   84.46%   +0.08%     
==========================================
  Files          27       27              
  Lines        2094     2099       +5     
==========================================
+ Hits         1767     1773       +6     
+ Misses        213      212       -1     
  Partials      114      114

Impacted Files	Coverage Δ
context.go	91.37% <100%> (+0.2%)	⬆️
echo.go	85.75% <0%> (+0.26%)	⬆️

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[djgilcrease]

I would make a MetricsContext interface with this in it, note the interface as potentially unstable while all the methods are determined for it and still have the default context implementation for the method. That way the default context satisfies both the Context and MetricsContext and people who want to get the metrics can cast the context. This also makes it so those who are implementing their own context do not break when this releases.

In v5 all the context interfaces could be merged if that is determined to be the best course.

[lammel]

@vishr Can you add the v5 label on this issue please

[vishr]

@lammel done!

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.