Support style/format checking on test phase

Description

Enforce formatting rules at test phase.

Implementation ideas

variables:
  MAVEN_FORMAT_TOOLS: com.spotify.fmt:fmt-maven-plugin:check
  # MAVEN_FORMAT_TOOLS: net.revelc.code.formatter:formatter-maven-plugin:validate

java-test-fmt:
  stage: test
  script:
    - if [[ -f "$JMAVEN_FORMAT_FILE" ]]; then
        export MAVEN_FORMAT_OPTS="${MAVEN_FORMAT_OPTS} -DconfigFile=${MAVEN_FORMAT_FILE}"
      fi
    - mvn ${MAVEN_FORMAT_TOOLS} ${MAVEN_FORMAT_OPTS}

revelc support a -DconfigFile parameters that should be compatible with a gitlab file variable.

Both plugin support a format goal, so it may be interesting to print out the format command when an error occured so the developer can fix it easily.