configuring with ff4j-config-yaml

[paul58914080]

As @clun reported in https://github.com/ff4j/ff4j-spring-boot-starter-parent/issues/106.

Consider other properties in the YAML ? like config. I said it because most of the work is already done in ff4j-config-yaml

https://github.com/ff4j/ff4j/blob/master/ff4j-config-yaml/src/test/java/org/ff4j/parser/yaml/YamlParserTest.java

InputStream ymlFile = getClass().getClassLoader().getResourceAsStream("application.yml");
FF4jConfiguration ymlConfig = new YamlParser().parseConfigurationFile(ymlFile);