move flutter to /opt

Dockerfile

 ARG IMAGE_SERVER="registry.420joos.dev"
 ARG FLUTTER_VERSION="3.24.5"
 ARG DEPENDENCY_DIR="/tmp/dependencies"
+ARG FLUTTER_DIR="opt/flutter"
 
 FROM ubuntu:24.04 AS download
 
 ARG FLUTTER_URL
 ARG FLUTTER_VERSION
 ARG DEPENDENCY_DIR
-ARG FLUTTER_DIR="$DEPENDENCY_DIR/flutter"
+ARG FLUTTER_DIR
+ARG FLUTTER_DIR="$DEPENDENCY_DIR/${FLUTTER_DIR}"
 ARG FLUTTER_DOWNLOAD_FILE="flutter.tar.xz"
 
 RUN apt update \
@@ -21,19 +23,21 @@ RUN mkdir -p ${FLUTTER_DIR} \
 FROM alpine:3.20.3
 
 ARG DEPENDENCY_DIR
+ARG FLUTTER_DIR
+
 ARG USER_UID="1000"
 ARG USER_GID=${USER_UID}
 ARG USERNAME="flutter"
 
-ENV FLUTTER_HOME="/flutter"
-ENV PATH=$PATH:$FLUTTER_HOME/bin
+ENV FLUTTER_DIR="/${FLUTTER_DIR}"
+ENV PATH=${PATH}:${FLUTTER_DIR}/bin
 
 COPY --from=download $DEPENDENCY_DIR /
 
 RUN apk add --no-cache bash git gcompat \
     && addgroup ${USERNAME} -g ${USER_GID} \
     && adduser ${USERNAME} --uid ${USER_UID} --ingroup ${USERNAME} --disabled-password \
-    && chown -R ${USERNAME}:${USERNAME} ${FLUTTER_HOME}
+    && chown -R ${USERNAME}:${USERNAME} ${FLUTTER_DIR}
 
 USER ${USERNAME}
 WORKDIR /home/${USERNAME}