[FEA] The Packager should create in the MAP the env var. MONAI_MODELPATH, with default

[MMelQin]

Is your feature request related to a problem? Please describe.
In the MONAI App Package, the models are placed in /opt/monai/models, and there is a env var per spec, MONAI_MODELPATH, whose default is set to the path of this folder. The application on startup, read this env var to find the folder to load the model files.

The Packager, for unknown reason, did not create this env var in the MAP container image, maybe it was expecting the defunct executor to manage this. In any case, to run the MPA as an container, the env var has to be passed in, even though the models are internal knowledge of the MAP, and the model default path need not be fiddled with.

Describe the solution you'd like
Add the step to create the env var, MONAI_MODELPATH with the default value /opt/monai/models, in the Dockerfile to generate the MAP.

Describe alternatives you've considered
The env var has to be passed in on docker run, e.g.
-e MONAI_MODELPATH="/opt/monai/models"

Additional context
All other env vars called for by the spec exist in the container image with the expected default.