Expose ProxySQL version in Docker image

[msladek]

The ProxySQL image Dockerfile receives the version through the build argument VERS and installs proxysql=${VERS}.

Because build arguments are not retained or inherited by derived images, could the image expose this value explicitly?

For example:

ARG VERS
ENV PROXYSQL_VERSION="${VERS}"

This would let derived images reliably discover the installed ProxySQL version.

[renecannao]

Good suggestion — agreed that exposing the version as an environment variable is useful for derived images and runtime introspection. I'll implement this with ENV PROXYSQL_VERSION="${VERS}" in both the Debian and CentOS Dockerfiles, along with a test to verify the variable is set correctly.