Bundle version 9 checklist #326

This issue is to keep track of my todo list for the bundle version 9 (intention is to target Symfony 9)

The plan is, as usual:

• A new version of the bundle is released shortly after Symfony 9 is officially released. This typically happens in the same time frame when a new PHP version is released as well. So please be patient, until work is finished.
• A 9.x branch will eventually appear, with an ⚠unstable development state. It is not recommended to be used in production scenarios, as there will a lot of changes and rebasing on this branch. Use it at your own risk.

Previous checklist for my own reference: #270

Todos

• Cleanup compatibility layer: Support the authentication proofs of Symfony 8.2 #322
• Change default number of digits for email authenticator to a more secure default
• Investigate if rate limiting can be safely activated per default