Dockerfile: Use eoan base image. Add missing python3 dependency for node-gyp.

Thanks to xet7 !

Dockerfile

@@ -1,10 +1,10 @@
-FROM ubuntu:disco
+FROM ubuntu:eoan
 LABEL maintainer="wekan"
 
 # Set the environment variables (defaults where required)
 # DOES NOT WORK: paxctl fix for alpine linux: https://github.com/wekan/wekan/issues/1303
 # ENV BUILD_DEPS="paxctl"
-ENV BUILD_DEPS="apt-utils bsdtar gnupg gosu wget curl bzip2 g++ build-essential git ca-certificates" \
+ENV BUILD_DEPS="apt-utils bsdtar gnupg gosu wget curl bzip2 g++ build-essential git ca-certificates python3" \
     DEBUG=false \
     NODE_VERSION=v8.16.2 \
     METEOR_RELEASE=1.8.1 \