Metrics is missing on frankenphp >= 1.4.0

### What happened?

`frankenphp_*` metrics were there  before v1.4.0

I did a quick debug and found out that caddy 2.9 changed the flow of how the module should hook to use the metrics registry
https://github.com/dunglas/frankenphp/blob/be2e4714f5624ba48824af07ad5e41ffafacda1b/caddy/caddy.go#L43 current frankenphp implementation is still relying on this https://github.com/caddyserver/caddy/pull/3709 but in https://github.com/caddyserver/caddy/commit/41f5dd56e1b93ec815daa98dd1f1caa7f2087312  (caddy v2.9.0) changed the flow to get the metrics registry

### Build Type

Docker (Debian Bookworm)

### Worker Mode

Yes

### Operating System

GNU/Linux

### CPU Architecture

x86_64

### PHP configuration

```shell
-
```

### Relevant log output

```shell
-
```

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Metrics is missing on frankenphp >= 1.4.0 #1365

What happened?

Build Type

Worker Mode

Operating System

CPU Architecture

PHP configuration

Relevant log output

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