https://github.com/git-commit-id/git-commit-id-maven-plugin/issues/701: Fix an issue with submodules

[TheSnoozer]

Context

This MR fixes an issue with submodules (see git-commit-id/git-commit-id-maven-plugin#701)

Needed changes:

• move the GitDirLocator from git-commit-id-maven-plugin to git-commit-id-plugin-core
• extended the Callback with shouldFailOnNoGitDirectory that determines if the execution should fail if no git directory can be extracted (please note that build information might now be populated since it is unrelated to git data)

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