fix: add missing 'CUSTOM_PROXY_HEADERS' var in Dockerfile

Signed-off-by: Robert Goniszewski <robertgoniszewski@outlook.com>

Dockerfile

@@ -23,6 +23,7 @@ ARG PORT=5173
 ARG PUBLIC_HTTPS_ONLY="false"
 ARG PUBLIC_SIGNUP_DISABLED="false"
 ARG BODY_SIZE_LIMIT="5000000"
+ARG CUSTOM_PROXY_HEADERS
 
 ENV PUBLIC_POCKETBASE_URL=$PUBLIC_POCKETBASE_URL
 ENV ROOT_ADMIN_EMAIL=$ROOT_ADMIN_EMAIL
@@ -33,6 +34,7 @@ ENV PORT=$PORT
 ENV PUBLIC_HTTPS_ONLY=$PUBLIC_HTTPS_ONLY
 ENV PUBLIC_SIGNUP_DISABLED=$PUBLIC_SIGNUP_DISABLED
 ENV BODY_SIZE_LIMIT=$BODY_SIZE_LIMIT
+ENV CUSTOM_PROXY_HEADERS=$CUSTOM_PROXY_HEADERS
 
 COPY --from=prod-deps /app/node_modules /app/node_modules
 COPY --from=build /app/build /app/build