Update apt commands per Docker recommendations...

Update apt commands per Docker recommendations https://docs.docker.com/develop/develop-images/dockerfile_best-practices/#run

dotnet-build-server/3.1/Dockerfile

@@ -13,8 +13,9 @@ LABEL org.label-schema.build-date=$BUILD_DATE \
       maintainer="Roger Feese <rfeese@nebraska.edu>"
 
 # Make sure that tools we need are installed
-RUN apt-get update \
-    && apt-get install git
+RUN apt-get update && apt-get install -y \
+    git \
+    && rm -rf /var/lib/apt/lists/*
 
 # sonarscanner (https://docs.sonarqube.org/latest/analysis/scan/sonarscanner-for-msbuild/)
 RUN dotnet tool install --global dotnet-sonarscanner

dotnet-build-server/5.0/Dockerfile

@@ -13,8 +13,9 @@ LABEL org.label-schema.build-date=$BUILD_DATE \
       maintainer="Roger Feese <rfeese@nebraska.edu>"
 
 # Make sure that tools we need are installed
-RUN apt-get update \
-    && apt-get install git
+RUN apt-get update && apt-get install -y \
+    git \
+    && rm -rf /var/lib/apt/lists/*
 
 # sonarscanner (https://docs.sonarqube.org/latest/analysis/scan/sonarscanner-for-msbuild/)
 RUN dotnet tool install --global dotnet-sonarscanner