XWiki fail to start with Postgresql

I found the issue, and unfortunately it's not an easy fix …

In order to initialize the main wiki, it's super important that we get to the end of this method : https://github.com/xwiki/xwiki-platform/blob/0fbb9e03ef836606177486f415e019b1933ce8e9/xwiki-platform-core/xwiki-platform-container/xwiki-platform-container-servlet/src/main/java/org/xwiki/container/servlet/XWikiServletContextListener.java#L136 ; in particular, it's important that every event listener that listens to ApplicationStartedEvent get executed before we actually try to fiddle with the main wiki initialization.

If we fail to wait for every event listener to be executed, we may run into WKINIT-3 for example. I initially tried to resolve the problem by explicitly calling event listener multiple times (https://github.com/xwiki-contrib/application-wiki-initializer/commit/dbfb65dea2e4de1dc45c84265fc632ebcb779962), but that ended up doing more harm than good …

So … the current solution from my POV will be to listen to the same ApplicationStartedEvent, and start a job with a 5 seconds delay (configurable) before actually initializing the main wiki. These 5 seconds should give plenty of time for the other event listeners to execute, and so that we have a clean context.

On the long run, it would be super nice to have another way to do this, maybe by having another event fired up, or by being able to prioritize event listeners (have one execute after the other). WDYT Thomas Mortagne ?

Added a 5 seconds delay by default to initialize the main wiki. This is configurable through the key wikiInitializer.mainWikiInitializationDelay (value should be given in miliseconds)