[Feature:Autograding] add image for gcc 11 (#60)

### What is the new behavior?

add dockerfile for gcc/g++ 11

---------

Co-authored-by: Barb Cutler <Barb Cutler>

Author: bmcutler

dockerfiles/gcc/11/Dockerfile

@@ -0,0 +1,10 @@
+FROM ubuntu:22.04
+
+# installing requirements to get and extract prebuilt binaries
+RUN apt-get update
+RUN apt-get install -y gcc-11 g++-11
+RUN rm -rf /var/lib/apt/lists/*
+
+# symlinks
+RUN ln -s /usr/bin/aarch64-linux-gnu-gcc-11 /usr/bin/gcc
+RUN ln -s /usr/bin/aarch64-linux-gnu-g++-11 /usr/bin/g++

dockerfiles/gcc/metadata.json

@@ -0,0 +1,4 @@
+{
+    "pushLatest": true,
+    "latestTag": "11"
+}