How do I automate a search across all repos to report .NET versions used?

[Christopher Carden]

I would like to be able to compile a list of all repos and their respective .NET versions in order to determine which, if any, are using an older version of .NET in need up upgrade (e.g., v 2.4).  This would be best if I could run the search via API or by calling a trigger to generate a report or output the response in some way, for remote access from a script or another app.