Update docker files to remove /root/.m2 directory after installation …

…to not distribute build dependencies (#200)

Part of security hardening: remove `/root/.m2` directory after the
installation has happened.

It seems like it's not needed as it keeps Maven cache, but we already
vendor all dependencies on `make install`.

This way we won't distribute any compile-time dependencies, reducing our
potential attack surface.

Dockerfile

@@ -10,4 +10,7 @@ COPY . /app
 WORKDIR /app
 RUN make clean install
 
+# Clean up build dependencies
+RUN rm -r /root/.m2
+
 ENTRYPOINT [ "/bin/bash" ]

Dockerfile.wolfi

@@ -56,6 +56,9 @@ ENV IS_DOCKER=1
 
 RUN make clean install
 
+# Clean up build dependencies
+RUN rm -r /root/.m2
+
 # ------------------------------------------------------------------------------
 # remove now-unnecessary packages and directories