Deprecate project; users should go to maven-executor instead

### Affected version

all

### Bug description

The maven-executor drop in replacement should be use that among other things offer smooth and transparent mvn3 and mvn4 support and same if not more functionality as maven-invoker and much more, like proper env isolation and so on.

The issue names no files, tests, or entry points. Start by reviewing the project and comparing its stated functionality with maven-executor, then determine the deprecation scope and communication needed; done means the project’s deprecation path is agreed and recorded.

Written by the indexing model from the issue text.