add dart 2.18 and 2.19

dart/2.18/Dockerfile

@@ -0,0 +1,14 @@
+FROM        --platform=$TARGETOS/$TARGETARCH dart:2.18
+
+LABEL       author="Alden Bansemer" maintainer="alden@knoban.com"
+
+RUN         apt update \
+            && apt -y install iproute2 git ca-certificates tzdata \
+            && useradd -m -d /home/container container
+
+USER        container
+ENV         USER=container HOME=/home/container
+WORKDIR     /home/container
+
+COPY        ./../entrypoint.sh /entrypoint.sh
+CMD         [ "/bin/bash", "/entrypoint.sh" ]