Move to Symfony Flex

The structure changed completely.
Bundles are gone. Everything is flatten in the folder `src`.
I separated import & api controllers to avoid _pollution_ in the main controller folder.

config/packages/cache.yaml

@@ -0,0 +1,19 @@
+framework:
+    cache:
+        # Unique name of your app: used to compute stable namespaces for cache keys.
+        #prefix_seed: your_vendor_name/app_name
+
+        # The "app" cache stores to the filesystem by default.
+        # The data in this cache should persist between deploys.
+        # Other options include:
+
+        # Redis
+        #app: cache.adapter.redis
+        #default_redis_provider: redis://localhost
+
+        # APCu (not recommended with heavy random-write workloads as memory fragmentation can cause perf issues)
+        #app: cache.adapter.apcu
+
+        # Namespaced pools use the above "app" backend by default
+        #pools:
+            #my.dedicated.cache: null