store/report ports tree version

[swills]

Need pkg repo metadata to store version of ports tree used to build packages and pkg command to return that info. See this thread:

https://lists.freebsd.org/pipermail/freebsd-ports/2020-August/119178.html

[evadot]

So we have source/source_identifier in the meta schema, it doesn't seems used and I wonder if it was planned to do something like that before ? cc @bapt

[bapt]

yes it was iirc.