Upgrade to PHP 8.4, make use of custom version optional

Re #1

.env.sample

@@ -4,19 +4,23 @@ DOMAIN=example.com
 ## Domain aliases
 #EXTRA_DOMAINS=', `www.example.com`'
 LETS_ENCRYPT_ENV=production
+COMPOSE_FILE=compose.yml
 
 ROOT_PATH=/var/www/html
-PHP_VERSION=7.4
 # environment (needed for PHP frameworks like laravel/symphony)
 APP_ENV=prod
 
+## Optional: Specify alternative PHP version
+#COMPOSE_FILE=$COMPOSE_FILE:compose.version.yml
+#PHP_VERSION=7.4-fpm-alpine
+
 ## Extra extensions you need (run `abra app YOURAPPDOMAIN run app "php -m"` to see active extensions)
 PHP_EXTENSIONS="pdo_mysql"
 ## Install libxslt, required for PHP `xsl` extension
 #INSTALL_XSL=1
 
 # Optional database
-#COMPOSE_FILE="compose.yml:compose.mariadb.yml"
+#COMPOSE_FILE="$COMPOSE_FILE:compose.mariadb.yml"
 SECRET_DB_ROOT_PASSWORD_VERSION=v1
 SECRET_DB_PASSWORD_VERSION=v1
 # Optionally override database name and password
@@ -25,12 +29,12 @@ SECRET_DB_PASSWORD_VERSION=v1
 
 
 # Local SMTP relay
-#COMPOSE_FILE="compose.yml:compose.mailrelay.yml"
+#COMPOSE_FILE="$COMPOSE_FILE:compose.mailrelay.yml"
 #SMTP_HOST="postfix_relay_app"
 #MAIL_FROM="site@example.com"
 
 # Remote SMTP relay
-#COMPOSE_FILE="compose.yml:compose.mailrelay.yml:compose.smtp.yml"
+#COMPOSE_FILE="$COMPOSE_FILE:compose.mailrelay.yml:compose.smtp.yml"
 #SMTP_HOST="mail.example.com"
 #MAIL_FROM="site@example.com"
 #SMTP_PORT=587

compose.version.yml

@@ -0,0 +1,6 @@
+---
+version: "3.8"
+
+services:
+  app:
+    image: php:${PHP_VERSION}

compose.yml

@@ -1,7 +1,7 @@
 version: "3.8"
 services:
   app:
-    image: php:${PHP_VERSION}-fpm-alpine3.13
+    image: php:8.4.3-fpm-alpine3.20
     volumes:
       - "site_content:/var/www/html/"
     networks: