Add formatter-maven-plugin to ensure file are well formatted.

[sbernard31]

formatter-maven-plugin allow to check code is well formatted with :

mvn formatter:validate

Code can be formatted with :

mvn formatter:format

The code format validation will be automatically done during build, when mvn clean install is called.

About "removing trailing spaces at end of the line" :
formatter-maven-plugin has an removeTrailingWhitespace option to handle it but only available since 2.17 which is not compatible with java8.
So waiting, I use maven-checkstyle-plugin to check this. (We will use checkstyle later for more than that)

All those will be automatically check on new PR using github actions. Errors will be reported like that : sbernard31#12