Prevent Logback from starting JsonProvider (remove Lifecycle interface)

[brenuart]

The JsonProvider interface currently extends Lifecycle. This means that Logback will call its start() method just after configuration properties are set. This is a standard pattern in the Logback ecosystem and works ok for most JsonProvider except a few like GlobalCustomFieldsJsonProvider and PatternJsonProvider.

These two providers need a JsonFactory to parse the value of some of their configuration properties. The factory is not provided by Logback but by the component to which the JsonProvider will be assigned. It is therefore not available at the time Logback calls the start() method. Parsing of the JSON properties is therefore delayed until a JsonFactory is set and will never happen during the lifecycle of component. As a comment already says in the source code, "parsing cannot occur during start() because the jsonFactory is not already set when Logback invokes the method".

Lifecycle of JsonProvider should be entirely delegated to the CompositeJsonFormatter or NestedJsonProvider to which they are assigned without Logback interfering at any time. These two components already call the start/stop method at the appropriate time and take care of assigning a JsonFactory before start() is invoked.

The conclusion is that JsonProvider(s) should not implement the Logback Lifecycle interface at all. This is totally useless since nothing will be done because the JsonFactory is not already set. This also makes the code more complex and moves the validation of the component state outside of the start() method where it usually goes.