revisit the way messages for password rotation policy are injected

[pmauduit]

Reading the following class: https://github.com/georchestra/georchestra-cas-server/blob/master/src/main/java/org/georchestra/cas/MessagesConfiguration.java I have the feeling that we are trying "to do something against what the framework provides us", and it does not read very "spring-ish":

• opening & parsing properties files by hand,
• using a CommandLineRunner for a feature which sounds more as a customization of the templates,
• dumping errors to stdout instead of using a logger,
• hardcoding a file path into the exploded webapp (what if we have a simple .war file which is not unzipped - e.g. jetty - into the expected path ?) ...

Also I think that the password rotation policy would deserve some tests or at least a "use-case docker composition" into the dedicated repository.

[pmauduit]

FTR, PR which introduced the change is here: https://github.com/georchestra/georchestra-cas-server/pull/14

[pmauduit]

See above commit for a sample docker composition to try the feature out