pecl8: command not found

Hello, I tried to install package opentelemetry without success.

The pecl extension was not found.

I tried following the manual with the following commands:

```
RUN apk add --no-cache $PHPIZE_DEPS \
&& pecl8 install opentelemetry
```

With the following return:

```
bash-5.1# apk add --no-cache $PHPIZE_DEPS \
&& pecl8 install opentelemetry
fetch https://dl-cdn.alpinelinux.org/alpine/v3.16/main/x86_64/APKINDEX.tar.gz
fetch https://dl-cdn.alpinelinux.org/alpine/v3.16/community/x86_64/APKINDEX.tar.gz
OK: 318 MiB in 147 packages
bash: pecl8: command not found
bash-5.1#
```

How to correctly install pecl?

Tks!

Start by reproducing the reported Alpine Docker commands, especially `apk add --no-cache $PHPIZE_DEPS` followed by `pecl8 install opentelemetry`, and inspect the image's PHP version and package setup. Done means the documented container build can locate PECL and install the OpenTelemetry extension successfully.

索引モデルが issue の本文から書いたものです。