Update dockerfile instructions

Dockerfile

@@ -2,7 +2,8 @@ FROM node:18-bookworm
 
 RUN apt-get update && \
     apt-get install -y \
-    graphicsmagick \
+    imagemagick \
+    ffmpeg \
     g++ \
     git \
     make
@@ -12,8 +13,7 @@ WORKDIR /server
 
 RUN rm -rf node_modules && \
     rm -f log/*.log && \
-    mkdir -p ./public/files/attachments/thumbnails && \
-    mkdir -p ./public/files/attachments/thumbnails2 && \
+    mkdir -p ./public/files/attachments && \
     yarn install
 
 ENV NODE_ENV production