Include required but missing VAR name and assignment in interpolation error message.
Include required but missing VAR name and assignment in interpolation error message.

Error message format is now e.g.:

ERROR: Missing mandatory value for "environment" option interpolating ['MYENV=${MYVAR:?}'] in service "myservice":

Fixed #6587.

Signed-off-by: Brett Randall <3a817d01b0aca4da51b95766d5e85950536c2c6e@gmail.com>

vdemeester/compose,vdemeester/compose,thaJeztah/compose,thaJeztah/compose