add docker compose setup for swift 5.8 (#29)

motivation: prepare for swift 5.8

changes:
* align base Dockerfile with lambda runtime
* add docker compose setup for nightly 5.8

Author: tomerd

docker/Dockerfile

@@ -1,4 +1,4 @@
-ARG swift_version=5.4
+ARG swift_version=5.7
 ARG base_image=swift:$swift_version-amazonlinux2
 FROM $base_image
 # needed to do again after FROM due to docker limitation
@@ -14,7 +14,7 @@ RUN echo 'export PATH="$HOME/.tools:$PATH"' >> $HOME/.profile
 
 # swiftformat (until part of the toolchain)
 
-ARG swiftformat_version=0.47.3
+ARG swiftformat_version=0.50.1
 RUN git clone --branch $swiftformat_version --depth 1 https://github.com/nicklockwood/SwiftFormat $HOME/.tools/swift-format
 RUN cd $HOME/.tools/swift-format && swift build -c release
 RUN ln -s $HOME/.tools/swift-format/.build/release/swiftformat $HOME/.tools/swiftformat

docker/docker-compose.al2.58.yaml

@@ -0,0 +1,18 @@
+version: "3"
+
+services:
+
+  runtime-setup:
+    image: swift-aws-lambda-events:al2-5.8
+    build:
+      args:
+        base_image: "swiftlang/swift:nightly-5.8-amazonlinux2"
+
+  test:
+    image: swift-aws-lambda-events:al2-5.8
+
+  test-samples:
+    image: swift-aws-lambda-events:al2-5.8
+
+  shell:
+    image: swift-aws-lambda-events:al2-5.8