Run docker dependency installation as root user

Dockerfile

@@ -2,7 +2,9 @@
 #for using with an existing container like shown in docker-compose.yml
 FROM mcr.microsoft.com/mssql/server:2022-latest
 ADD nodirect_open.c /
+USER root
 RUN apt update && apt install -y gcc && \
     gcc -shared -fpic -o /nodirect_open.so nodirect_open.c -ldl && \
     apt purge -y gcc && \
     echo "/nodirect_open.so" >> /etc/ld.so.preload
+USER mssql