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%)	⬆️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 1ac4a8f...78a0ea2. Read the comment docs.