🐛 requestid.Config.ContextKey is interface{} (#2369)

requestid.Config.ContextKey is interface{}

Consistent with c.Locals(key inteface{}, ...).
Fixes #2356

docs/api/middleware/requestid.md

@@ -61,7 +61,7 @@ type Config struct {
     // the locals for a specific request.
     //
     // Optional. Default: requestid
-    ContextKey string
+    ContextKey interface{}
 }
 ```
 

middleware/requestid/config.go

@@ -26,7 +26,7 @@ type Config struct {
 	// the locals for a specific request.
 	//
 	// Optional. Default: requestid
-	ContextKey string
+	ContextKey interface{}
 }
 
 // ConfigDefault is the default config

middleware/requestid/requestid_test.go

@@ -55,20 +55,21 @@ func Test_RequestID_Next(t *testing.T) {
 func Test_RequestID_Locals(t *testing.T) {
 	t.Parallel()
 	reqID := "ThisIsARequestId"
-	ctxKey := "ThisIsAContextKey"
+	type ContextKey int
+	const requestContextKey ContextKey = iota
 
 	app := fiber.New()
 	app.Use(New(Config{
 		Generator: func() string {
 			return reqID
 		},
-		ContextKey: ctxKey,
+		ContextKey: requestContextKey,
 	}))
 
 	var ctxVal string
 
 	app.Use(func(c *fiber.Ctx) error {
-		ctxVal = c.Locals(ctxKey).(string) //nolint:forcetypeassert,errcheck // We always store a string in here
+		ctxVal = c.Locals(requestContextKey).(string) //nolint:forcetypeassert,errcheck // We always store a string in here
 		return c.Next()
 	})