Make ENV instructions from Dockerfile work as env variable in walt image

[finieluga]

How to reproduce:

• Create a Dockerfile with an ENV instruction to define an environment variable (e.g., modifying the PATH).
• Build the image using the walt image build command.
• Boot a node using the newly built image via walt node boot.
• Connect to the node using walt node shell.
• Check the environment variable with a command like echo $PATH.

Expected behavior:

The environment variable defined via the ENV instruction should be available in the shell when connected to the node.

Actual behavior:

The environment variable is not set or updated when connecting to the node shell.

Investigation:

In Docker, the ENV instruction adds metadata to the image (visible with docker image inspect), but it does not directly modify files in the image filesystem.

As a workaround, the environment variable can be explicitly set in the image by modifying the .bashrc file.

Suggested improvement:

Automatically generate a script in /etc/profile.d/ during the image build process to expose environment variables defined via ENV instructions.