Update to Ubuntu 22.04 and allow running docker image as user that's …

…not ethsigner

docker/Dockerfile

@@ -9,7 +9,7 @@ RUN JAVA_TOOL_OPTIONS="-Djdk.lang.Process.launchMechanism=vfork" "$JAVA_HOME/bin
          --compress=2 \
          --output /javaruntime
 
-FROM ubuntu:21.10
+FROM ubuntu:22.04
 ENV JAVA_HOME=/opt/java/openjdk
 ENV PATH "${JAVA_HOME}/bin:${PATH}"
 COPY --from=jre-build /javaruntime $JAVA_HOME
@@ -20,7 +20,8 @@ RUN apt update && apt install -y --no-install-recommends curl iputils-ping net-t
 
 # Add ethsigner user instead of using root (may bring backward incompatibility for previous directory mounts)
 RUN adduser --disabled-password --gecos "" --home /opt/ethsigner ethsigner && \
-    chown ethsigner:ethsigner /opt/ethsigner
+    chown ethsigner:ethsigner /opt/ethsigner && \
+    chmod 755 /opt/ethsigner
 USER ethsigner
 WORKDIR /opt/ethsigner