[MWRAPPER-99] Support MAVEN_ARGS environment variable

**[Piotr Karwasz](https://issues.apache.org/jira/secure/ViewProfile.jspa?name=pkarwasz)** opened **[MWRAPPER-99](https://issues.apache.org/jira/browse/MWRAPPER-99?redirect=false)** and commented

Starting with Maven 3.9.0 the `mvn/mvn.cmd` scripts support a `MAVEN_ARGS` environment variable that can be used to pass additional arguments to Maven (cf. [documentation](https://maven.apache.org/configure.html)).

The (undocumented?) `MAVEN_CONFIG` variable plays the same role in the `mvnw/mvnw.cmd` scripts.

Maven Wrapper should probably switch to `MAVEN_ARGS` as variable name (maintaining backward compatibility).

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**Affects:** 3.1.1

**Issue Links:**
- [MWRAPPER-61](https://issues.apache.org/jira/browse/MWRAPPER-61) let mvnw call mvn directly, without maven-wrapper.jar

- [MWRAPPER-125](https://issues.apache.org/jira/browse/MWRAPPER-125) Make "only-script" the default wrapper

- [MWRAPPER-45](https://issues.apache.org/jira/browse/MWRAPPER-45) Migrate/Sync startup scripts with Maven 4

Start by comparing the mvnw and mvnw.cmd scripts with the corresponding mvn and mvn.cmd behavior described in the Maven configuration documentation. Trace how MAVEN_CONFIG is currently consumed and identify the compatibility behavior needed for MAVEN_ARGS. Done means the wrapper accepts the newer variable without breaking existing MAVEN_CONFIG users.

Written by the indexing model from the issue text.