Adds RequestIDHandler function to RequestID middleware

[zacscoding]

Adds RequestIDHandler function in RequestID middleware to use the value.
For example, suppose we want to use RequestID value in logger after extract.

e.Use(RequestIDWithConfig(RequestIDConfig{
	RequestIDHandler: func(ctx echo.Context, requestID string) {
		logger := logging.DefaultLogger().With("x-request-id", requestID)
		ctx.SetRequest(ctx.Request().WithContext(logging.WithLogger(logger)))
	},
}))

[codecov]

Codecov Report

Merging #1898 (78a0ea2) into master (1ac4a8f) will increase coverage by 0.33%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #1898      +/-   ##
==========================================
+ Coverage   90.61%   90.94%   +0.33%     
==========================================
  Files          31       31              
  Lines        2782     2784       +2     
==========================================
+ Hits         2521     2532      +11     
+ Misses        168      161       -7     
+ Partials       93       91       -2     

Impacted Files	Coverage Δ
middleware/request_id.go	84.21% <100.00%> (+1.85%)	⬆️
router.go	95.69% <0.00%> (+0.66%)	⬆️
echo.go	93.80% <0.00%> (+2.16%)	⬆️

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