Feat: Pull out maven-executor into its own project (#12004)

The main goal of `maven-executor` is ability to execute Maven 3/4 in "embedded" and "forked" mode, and has not related with Maven release lifecycle itself (and is dependency-less as well). So, let's move it out into own project.

https://github.com/apache/maven-executor

The new library executes Maven in:
* forked or embedded mode, but introduces other providers as well
* supports Maven 3 and 4
* the main `maven-executor` module is Java 8, dependency-less library (is MR-JAR, and on 9+ is modular and provides ToolProvider SPI integration as well)

Author: cstamas

.mvn/maven.config

@@ -1 +1,4 @@
--DsessionRootDirectory=${session.rootDirectory}
+-D
+sessionRootDirectory=${session.rootDirectory}
+-D
+apache.snapshots