Lock examples to PostgreSQL 16

Signed-off-by: Kaloyan Nikolov <tzerber@gmail.com>

.examples/docker-compose/insecure/postgres/apache/compose.yaml

@@ -2,7 +2,7 @@ services:
   # Note: PostgreSQL is an external service. You can find more information about the configuration here:
   # https://github.com/docker-library/docs/blob/master/postgres/README.md
   db:
-    image: postgres:alpine
+    image: postgres:16-alpine
     restart: always
     volumes:
       - db:/var/lib/postgresql/data:Z

.examples/docker-compose/insecure/postgres/fpm/compose.yaml

@@ -2,7 +2,7 @@ services:
   # Note: PostgreSQL is an external service. You can find more information about the configuration here:
   # https://github.com/docker-library/docs/blob/master/postgres/README.md
   db:
-    image: postgres:alpine
+    image: postgres:16-alpine
     restart: always
     volumes:
       - db:/var/lib/postgresql/data:Z

.examples/docker-compose/with-nginx-proxy/postgres/apache/compose.yaml

@@ -2,7 +2,7 @@ services:
   # Note: PostgreSQL is an external service. You can find more information about the configuration here:
   # https://github.com/docker-library/docs/blob/master/postgres/README.md
   db:
-    image: postgres:alpine
+    image: postgres:16-alpine
     restart: always
     volumes:
       - db:/var/lib/postgresql/data:Z

.examples/docker-compose/with-nginx-proxy/postgres/fpm/compose.yaml

@@ -2,7 +2,7 @@ services:
   # Note: PostgreSQL is an external service. You can find more information about the configuration here:
   # https://github.com/docker-library/docs/blob/master/postgres/README.md
   db:
-    image: postgres:alpine
+    image: postgres:16-alpine
     restart: always
     volumes:
       - db:/var/lib/postgresql/data:Z