feat(caddy): upgrade to Caddy 2.9.0

[dunglas]

Upgrade to Caddy 2.9 and leverage the new first_exist_fallback try policy (caddyserver/caddy#6699).

[AlliBalliBaba]

@dunglas I noticed that this block will also cause a file access on every request even though its only purpose is to redirect on directory index files from /path -> /path/ (the 'canonical' path). Not sure how to optimize this, but it would be another opportunity to minimize file access.

https://github.com/dunglas/frankenphp/blob/c2ca4dbf03048d7d82c9b069646d64d1454b6abb/caddy/caddy.go#L559-L582

[dunglas]

Yes, I already discussed this one with @francislavoie but I'm not sure we can find a generic solution to prevent it.

The best we can do is probably some custom config like this one, or to introduce a cache. https://github.com/dunglas/symfony-docker/blob/main/frankenphp/Caddyfile