add docker file for swift 5.5 (#3661)

motivation: keep with the times

changes:
* update 5.4 docker file to use the release version instead of the development one
* add a 5.5 dockerfile

Author: tomerd

Utilities/Docker/docker-compose.2004.54.yaml

@@ -16,7 +16,6 @@ services:
       args:
         ubuntu_version: "focal"
         swift_version: "5.4"
-        base_image: "swiftlang/swift:nightly-5.4-focal"
 
   build:
     image: swift-package-manager:20.04-5.4

Utilities/Docker/docker-compose.2004.55.yaml

@@ -0,0 +1,37 @@
+# This source file is part of the Swift.org open source project
+#
+# Copyright (c) 2021 Apple Inc. and the Swift project authors
+# Licensed under Apache License v2.0 with Runtime Library Exception
+#
+# See http://swift.org/LICENSE.txt for license information
+# See http://swift.org/CONTRIBUTORS.txt for Swift project authors
+
+version: "3"
+
+services:
+
+  runtime-setup:
+    image: swift-package-manager:20.04-5.5
+    build:
+      args:
+        ubuntu_version: "focal"
+        swift_version: "5.5"
+        base_image: "swiftlang/swift:nightly-5.5-focal"
+
+  build:
+    image: swift-package-manager:20.04-5.5
+
+  test:
+    image: swift-package-manager:20.04-5.5
+
+  bootstrap-clean:
+    image: swift-package-manager:20.04-5.5
+
+  bootstrap-build:
+    image: swift-package-manager:20.04-5.5
+
+  bootstrap-test:
+    image: swift-package-manager:20.04-5.5
+
+  shell:
+    image: swift-package-manager:20.04-5.5