Git path is not updated and verified during adding 2+ IDF

[georgik]

The git path is stored to JSON file in idf-env config command only during the first installation.
When user move tools to other location and runs the installer then the path is the same which may result in problem with starting terminal, because git binary was not found.

Expected behaviour: idf-env config will update JSON file and check whether git exists.

If no git was detected on the defined path, it might be worthy to consider adding git from System PATH.