[SCB-611]Provide URLMappedEdgeDispatcher to using edge service easier

[liubao68]

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[coveralls]

Coverage decreased (-0.02%) to 87.505% when pulling 7884277 on liubao68:master into 6ce5280 on apache:master.

[liubao68]

Documents: https://github.com/apache/incubator-servicecomb-docs/pull/4/files