feat: deprecate python 3.7 #2 (#1582)
- previous deprecation of Ptyhon 3.7 in models did not have actual check (feat: deprecate python 3.7 #1550);
- now the model python minimum version is checked in cog build only;
- this new approach is compatible with existing already built and/or uploaded models;
- fixed integration test;
- keep running CI tests on python 3.7;
