[CI] Add docker compose setup for 5.5 (#410)

Author: tomerd

Diff for: docker/docker-compose.2004.55.yaml

@@ -0,0 +1,18 @@
+version: "3"
+
+services:
+        
+  runtime-setup:
+    image: async-http-client:20.04-5.5
+    build:
+      args:
+        base_image: "swiftlang/swift:nightly-5.5-focal"
+        
+
+  test:
+    image: async-http-client:20.04-5.5
+    environment: []
+      #- SANITIZER_ARG=--sanitize=thread
+
+  shell:
+    image: async-http-client:20.04-5.5