Install .NET SDKs from blob storage instead of package manager

src/unix/docker/dockerfiles/build/ubuntu/Dockerfile

@@ -4,26 +4,51 @@
 # This image is based on the public Ubuntu 18.04 LTS image
 FROM mcr.microsoft.com/mirror/docker/library/ubuntu:18.04@sha256:152dc042452c496007f07ca9127571cb9c29697f42acbfad72324b2bb2e43c98
 
+# REFERENCE: https://github.com/dotnet/dotnet-docker/blob/main/src/sdk/6.0/jammy/amd64/Dockerfile
+
+ENV \
+    # Do not generate certificate
+    DOTNET_GENERATE_ASPNET_CERTIFICATE=false \
+    # Do not show first run text
+    DOTNET_NOLOGO=true \
+    # .NET 6 SDK version
+    DOTNET_6_SDK_VERSION=6.0.427 \
+    # .NET 7 SDK version
+    DOTNET_7_SDK_VERSION=7.0.410 \
+    # Enable correct mode for dotnet watch (only mode supported in a container)
+    DOTNET_USE_POLLING_FILE_WATCHER=true \
+    # Skip extraction of XML docs - generally not useful within an image/container - helps performance
+    NUGET_XMLDOC_MODE=skip
+
 RUN apt-get update \
     && apt-get install -y --no-install-recommends \
         ca-certificates \
         curl \
-        software-properties-common
-
-# Install .NET SDKs
-# https://learn.microsoft.com/en-us/dotnet/core/install/linux-ubuntu#register-the-microsoft-package-repository
-RUN curl -SL --output packages-microsoft-prod.deb https://packages.microsoft.com/config/ubuntu/18.04/packages-microsoft-prod.deb \
-    && dpkg -i packages-microsoft-prod.deb \
-    && rm packages-microsoft-prod.deb
-
-RUN apt-get install -y --no-install-recommends apt-transport-https \
-    && apt-get update \
-    && apt-get install -y --no-install-recommends \
-        dotnet-sdk-6.0 \
-        dotnet-sdk-7.0
+        libicu60 \
+        # Needed for "apt-add-repository" later in Dockerfile
+        software-properties-common \
+        wget \
+    && rm -rf /var/lib/apt/lists/*
 
-# Trigger first run experience by running arbitrary cmd to populate local package cache
-RUN dotnet help
+RUN \
+    # Install .NET 6 SDK
+    curl -fSL --output dotnet.tar.gz https://dotnetcli.azureedge.net/dotnet/Sdk/$DOTNET_6_SDK_VERSION/dotnet-sdk-$DOTNET_6_SDK_VERSION-linux-x64.tar.gz \
+    && dotnet_sha512='a9cd1e5ccc3c5d847aca2ef21dd145f61c6b18c4e75a3c2fc9aed592c6066d511b8b658c54c2cd851938fe5aba2386e5f6f51005f6406b420110c0ec408a8401' \
+    && echo "$dotnet_sha512  dotnet.tar.gz" | sha512sum -c - \
+    && mkdir -p /usr/share/dotnet \
+    && tar -oxzf dotnet.tar.gz -C /usr/share/dotnet \
+    && rm dotnet.tar.gz \
+    # Install .NET 7 SDK
+    && curl -fSL --output dotnet.tar.gz https://dotnetcli.azureedge.net/dotnet/Sdk/$DOTNET_7_SDK_VERSION/dotnet-sdk-$DOTNET_7_SDK_VERSION-linux-x64.tar.gz \
+    && dotnet_sha512='20b8e02979328e4c4a14493f7791ed419aabd0175233db80cd60e2c004b829b3e8301281ea86b27ba818372473accf5a6d553e5354c54917c8e84d25f5855caa' \
+    && echo "$dotnet_sha512  dotnet.tar.gz" | sha512sum -c - \
+    && mkdir -p /usr/share/dotnet \
+    && tar -oxzf dotnet.tar.gz -C /usr/share/dotnet \
+    && rm dotnet.tar.gz \
+    # Make dotnet symlink
+    && ln -s /usr/share/dotnet/dotnet /usr/bin/dotnet \
+    # Trigger first run experience by running arbitrary cmd
+    && dotnet help
 
 RUN echo 'export DOTNET_ROOT=$HOME/.dotnet' >> ~/.bashrc
 RUN echo 'export DOTNET_EXE=$DOTNET_ROOT/dotnet' >> ~/.bashrc