As counterpart to maven.repo.local.tail, but this one "prepends" while other "appends". This means one can do like this
```
$ mvn install -Prun-its -Dmaven.repo.local.head=~/.m2/repository-it
```
And have stuff installed into dedicated IT local repo (as IT bits must be installed), instead to pollute own local repo.
---
https://issues.apache.org/jira/browse/MNG-8370
To have them listed in generated docs, as they were forgotten.
Also, adding a "compat" support for Maven 3.9.x property for chained reposes.
---
https://issues.apache.org/jira/browse/MNG-8362