…iles

To make sure that all pom.xml files follow the same convention regarding
indentation and organization, add spotless plugin with sortPom module to
check and format the files automatically.

Update Java developer documentation to provide the link to the
convention and instructions on how to use spotless

*Note* this change does not include changes to pom.xml files (and would
fail the build. Changes to pom.xml files are in the next commit.

Apply spotless formatter to all pom.xml files

Downgrate spotless to 2.30.0 (last java 8 release)