Add sqlcmd and bcp to $PATH

[cezarlamann]

First, I'd like to thank you for all the effort you guys put into maintaining this image.

From the issue title: Could you either add /opt/mssql-tools18/bin to the $PATH or symlink both sqlcmd and bcp to /usr/bin?

This would avoid breaking images that were relying on the previous path /opt/mssql-tools/bin, and having us to worry about where would sqlcmd and bcp be after an image gets updated with new versions from the tools.

This would be a significant QOL improvement for everyone who depends on this image for our workloads.

Thank you.

[cezarlamann]

#898
#894
#892