[3.10] Consider user wide properties too

### New feature, improvement proposal

This is just a faint idea, as 3.10 is wildly different than 4.0 regarding properties, and this may introduce feature disparity, like user-wide maven.config, where 4.0 would use maven.properties?

All in all, goals:
* be able to define user wide properties
* do not break feature parity, if possible

Start by comparing how Maven 3.10 and 4.0 currently handle properties, with particular attention to the stated maven.config and maven.properties disparity. Done means defining a user-wide property mechanism while preserving feature parity where possible.

Written by the indexing model from the issue text.