Integrate new PHP version for local development

Make the image slightly smaller by removing the older PHP versions.
Start using the latest version for faster PHP. In domjudge/domjudge CI
we use the lowest supported one so we catch the whole spectrum.

docker-contributor/Dockerfile

@@ -12,8 +12,8 @@ ENV DEBIAN_FRONTEND=noninteractive \
   FPM_MAX_CHILDREN=40 \
   DJ_SKIP_MAKE=0 \
   DJ_DB_INSTALL_BARE=0 \
-  PHPSUPPORTED="7.2 7.3 7.4 8.0 8.1 8.2" \
-  DEFAULTPHPVERSION="8.1" \
+  PHPSUPPORTED="8.0 8.1 8.2 8.3" \
+  DEFAULTPHPVERSION="8.3" \
   APTINSTALL="apt install -y -o Dpkg::Options::=--force-confdef -o Dpkg::Options::=--force-confold"
 
 # Install required packages and clean up afterwards to make this image layer smaller