Update CE/SP base image to phusion `focal-1.0.0` (#5502)

GitOrigin-RevId: c87acddcdad22e0b5f5fbe28f6c57e13629a9cdd

server-ce/Dockerfile-base

@@ -2,7 +2,7 @@
 # Overleaf Base Image (sharelatex/sharelatex-base)
 # --------------------------------------------------
 
-FROM phusion/baseimage:0.11
+FROM phusion/baseimage:focal-1.0.0
 
 # Makes sure LuaTex cache is writable
 # -----------------------------------