Add Date Modified (Installed/Updated) to JSON Objects

[Justintime50]

It'd be awesome for debugging purposes if we could also show the date a package was installed/updated in an environment alongside the other details:

https://stackoverflow.com/questions/24736316/see-when-packages-were-installed-updated-using-pip

This came up recently when trying to debug dependencies of dependencies that were not pinned and trying to determine which of the recently randomly updated dependencies broke our builds.