Copy consolidated path for openapi spec

[Inozuma]

There is currently an issue when using a router group and a tonic handler together. The path is consolidated for the openapi spec operation (but only in case there is a tonic handler), but overrides the path which is later used to declare the route on the underlying gin router.

For example:

r := fizz.New()
g := r.Group("/test", "test", "test group")
g.GET("", tonic.Handler(func (c *gin.Context, in *Input) error {
  ...
}))

This example will declare a route in gin as /test/test instead of just /test.

[codecov[bot]]

Codecov Report

Merging #30 into master will not change coverage. The diff coverage is 100%.

@@          Coverage Diff           @@
##           master     #30   +/-   ##
======================================
  Coverage    96.7%   96.7%           
======================================
  Files           7       7           
  Lines         942     942           
======================================
  Hits          911     911           
  Misses         18      18           
  Partials       13      13

Impacted Files	Coverage Δ
fizz.go	98.8% <100%> (ø)	:arrow_up:

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