apply spotless code-style formatter and header-license builder also

[spaceluke]

What's the purpose of this PR

See #5480

Brief changelog

1. apply spotless code-style formatter plugin at pom.xml
2. add header-license to control also
3. apply the code formatter

Suggest remain this PR for 2-4 weeks, I will review it when I was slacking off at work.

Next step is append checker to CI-workflow

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• Update the CHANGES log.

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✨ Finishing touches

• 📝 Generate docstrings

🧪 Generate unit tests (beta)

• Create PR with unit tests
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[spaceluke]

@nobodyiam
I think these formatting steps are generally in line with our expectations, except for some minor issues with code comments, but that's fine～ we can improve them by configuring XML.

Should we format the comments and java-doc ?

I think to add a space between '//' and comments would be nice:

Is these change appropriate as well?

My idea is to retain the original multi-line comments in the docs, but format the single-line "//" comments.

by setting xml:

<setting id="org.eclipse.jdt.core.formatter.comment.format_block_comments" value="false"/>
<setting id="org.eclipse.jdt.core.formatter.comment.format_line_comments" value="true"/>
<setting id="org.eclipse.jdt.core.formatter.comment.format_javadoc_comments" value="false"/>

My incorrect rebase operation seems to have messed up this branch; I'll create a new branch to do the work. 🥶