#465: relocate the group-id and artifact-id of the maven-plugin

[TheSnoozer]

relocate the maven-plugin from

<groupId>pl.project13.maven</groupId>
<artifactId>git-commit-id-plugin</artifactId>

to

<groupId>io.github.git-commit-id</groupId>
<artifactId>git-commit-id-maven-plugin</artifactId>

See #465 for details.

Context

Contributor Checklist

• Added relevant integration or unit tests to verify the changes
• Update the Readme or any other documentation (including relevant Javadoc)
• Ensured that tests pass locally: mvn clean package
• Ensured that the code meets the current checkstyle coding style definition: mvn clean verify -Pcheckstyle -Dmaven.test.skip=true -B

[TheSnoozer]

TODO for myself: Enhance Readme with references to OLD and NEW group+artifact combo.