Implements api routes and api key auth

CAUTION: Temporary api key is hardcoded, must be changed

internal/api/api.go

@@ -0,0 +1,20 @@
+package api
+
+import (
+	"github.com/gofiber/fiber/v2"
+	"github.com/gofiber/fiber/v2/middleware/keyauth"
+)
+
+func Setup(app *fiber.App) {
+	api := app.Group("/api", keyauth.New(keyauth.Config{
+		SuccessHandler: successHandler,
+		ErrorHandler:   errHandler,
+		KeyLookup:      "header:x-api-key",
+		ContextKey:     "apiKey",
+		Validator:      validateAPIKey,
+	}))
+
+	v1 := api.Group("/v1")
+
+	v1.Get("/users", FetchAllUsersHandler)
+}