[Feature] Move away from __version__ to signify atlas minor version in packaging scripts.

[alessandrofelder]

Is your feature request related to a problem? Please describe.
IIUC correctly we are not using __version__ appropriately in atlas packaging scripts.

• it is supposed to related to the module
• it is confusing because we use it to relate to the minor version of the atlas, and not the full version as the variable name might imply

Describe the solution you'd like
The atlas major and minor versions should be handled in the same way as other metadata, instead of using a Python module attribute.