Enable scalable handlerID with GetPathTemplate support

[nwadams]

Would it be possible to add an option to use GetPathTemplate in gorilla, or similar in other libraries instead of the exact url route when initialized with mdwr.Handler("", h). This will allow more scalable path tracking to generalize ID params and avoid high tag cardinality explosion.

If you want I can investigate making this change if you are willing to accept a PR.

[matino]

That would be great indeed.