Make ca-certificates dependency explicit

ca-certificates-bundle (which provides /etc/ssl/certs/ca-certificates.crt)
is already pulled in transitively by apache2 / php-apache2 on alpine:3.23,
so live HTTPS calls from PHP work today (verified with file_get_contents
against ipinfo.io). But the master image (FROM php:8-alpine) installs
the full ca-certificates package explicitly, and operators with
IPINFO_APIKEY configured rely on outbound HTTPS. Make the dependency
explicit to:

* Match master's package set rather than relying on a transitive pull
  that some future apk dep change could drop.
* Document the runtime TLS requirement at the Dockerfile level instead
  of leaving it implicit.

~50 KB image-size cost; the umbrella ca-certificates package adds the
update-ca-certificates CLI on top of the bundle. Per Qodo's review on
PR #800.

Dockerfile.alpine

@@ -2,6 +2,7 @@ FROM alpine:3.23
 RUN apk add --quiet --no-cache \
     bash \
     apache2 \
+    ca-certificates \
     php \
     php-apache2 \
     php-ctype \