[MRELEASE-1054] Support for excluding submodules changes.

[wuwen5]

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As described in [MRELEASE-1054], when I use the Git submodule in a project, release: prepare will fail. I really need to support the release of the Git submodule, and I also have a pull request in the maven-scm project apache/maven-scm#179.

[wuwen5]

@elharo I have addressed the issues you pointed out, and I kindly request you to review the modified code. If you have any further suggestions or if there are additional changes needed, please let me know.

done