Removal of engine (gin) default settings (e.g. RedirectFixedPath)

[mdaur]

Describe the bug In case of the usage of the gin engine, the setting RedirectFixedPath breaks any middleware including NoRoute (default 404) handlers and panics (see router/gin/router.go ).

To Reproduce Steps to reproduce the behavior:

1. Usage of gin engine (gin.Default()) in any NewFactory (e.g. https://github.com/devopsfaith/krakend-examples/tree/master/gin/)
2. Request for non lura URI e.g. /not-there

Expected behavior Execution of NoRoute handler (in case of gin.Default()) and any configured middleware

Logs 2021/07/11 11:16:12 http: panic serving 127.0.0.1:48994: invalid node type goroutine 133 [running]: net/http.(*conn).serve.func1(0xc0000c4dc0) /opt/go1.16.linux-amd64/src/net/http/server.go:1824 +0x153 panic(0xf85140, 0x11ba830) /opt/go1.16.linux-amd64/src/runtime/panic.go:971 +0x499 github.com/gin-gonic/gin.(*node).findCaseInsensitivePathRec(0xc0002ef340, 0xc0006921e4, 0xc, 0xc000530080, 0x0, 0x80, 0x100000000, 0xc0000ae201, 0xc0000298c0, 0x0) /home/lhgdam4/go/pkg/mod/github.com/gin-gonic/[email protected]/tree.go:790 +0x109b github.com/gin-gonic/gin.(*node).findCaseInsensitivePath(0xc0002ef340, 0xc0006921e4, 0xc, 0x1, 0xc, 0x203000, 0x9, 0x1) /home/lhgdam4/go/pkg/mod/github.com/gin-gonic/[email protected]/tree.go:597 +0xb6 github.com/gin-gonic/gin.redirectFixedPath(0xc000344400, 0xc0002ef340, 0x1, 0xc00050e1b0) /home/lhgdam4/go/pkg/mod/github.com/gin-gonic/[email protected]/gin.go:557 +0x77 github.com/gin-gonic/gin.(*Engine).handleHTTPRequest(0xc00010e680, 0xc000344400) /home/lhgdam4/go/pkg/mod/github.com/gin-gonic/[email protected]/gin.go:498 +0x60d github.com/gin-gonic/gin.(*Engine).ServeHTTP(0xc00010e680, 0x11dc1f0, 0xc0005a4540, 0xc000344300) /home/lhgdam4/go/pkg/mod/github.com/gin-gonic/[email protected]/gin.go:445 +0x15c net/http.serverHandler.ServeHTTP(0xc0003ac2a0, 0x11dc1f0, 0xc0005a4540, 0xc000344300) /opt/go1.16.linux-amd64/src/net/http/server.go:2887 +0xa3 net/http.(*conn).serve(0xc0000c4dc0, 0x11ddb80, 0xc00004a480) /opt/go1.16.linux-amd64/src/net/http/server.go:1952 +0x8cd created by net/http.(*Server).Serve /opt/go1.16.linux-amd64/src/net/http/server.go:3013 +0x39b

Additional context If someone still depend on this setting, it would be wise to set it right after gin.Default() and before the NewFactory gets called.