Make mvnd download Maven version specified by Maven Wrapper configuration

currently, mvnd ships with an embedded Maven version in it: this leads to questions on how to have a mvnd release for each Maven release, with a clear pattern #392

it would be nice if Maven version was not injected at mvnd build time but at runtime: to avoid reinventing a wheel, the Maven Wrapper configuration `.mvn/wrapper/maven-wrapper.properties` could be used to define per-project target Maven

Start by tracing where mvnd currently selects or embeds its Maven version, then compare that flow with the `.mvn/wrapper/maven-wrapper.properties` configuration named in the issue. The work is done when a project’s wrapper configuration determines the Maven version downloaded and used at runtime, rather than requiring the version at mvnd build time.

Written by the indexing model from the issue text.