feat: change method of getting version from setup.py to package.xml

[h-suzuki-isp]

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[ymski]

@h-suzuki-isp
It seems to be working well. For a better fix, check the following comments.

• Package.xml is referenced when obtaining version information. When extracting version information from package.xml, you may want to consider using xml.etree.ElementTree instead of text analysis.

• You may need to add <exec_depend>ament_index_python</exec_depend> to package.xml.

[ymski]

LGTM