Allow the OpenID provider to register itself as the default authenticator directly upon install

The idea for this issue is to help with the provisioning of a wiki through an automated process.

It is already possible, by setting-up the default UI of a wiki, as well as running the distribution wizard non-interactively, to skip the whole bootstrap process of an XWiki instance. When it comes to the setup of the OpenID authenticator, we can automate the installation of the extension, but we cannot automatically register the OIDC connector as the default authentication provider.

The idea of this issue would be to have :

• A configuration key, such as oidc.registerAuthenticatorOnInstall or oidc.registerAuthenticatorAutomatically, to define if the feature should be enabled by default
• A listener on ExtensionInstalledEvent (possibly on ApplicationReadyEvent also if we go with oidc.registerAuthenticatorAutomatically) to automatically update the AuthClass to be used by XWiki

I'd be interested to know from other maintainers how they feel about this feature, before bundling it.