docker image: Change base to Ubuntu 22.04 LTS (jammy) (#1135)

Done to upgrade from CMake 3.16.3 to 3.22.1. CMake 3.21 or newer is needed to build the Qt 6.4.1 sources with emscripten.

Also update to libidn12 to resolve an "Unable to locate package libidn11" error.

docker/Dockerfile

diff --git a/docker/Dockerfile b/docker/Dockerfile
index bc201e1..508d7b3 100644
--- a/docker/Dockerfile
+++ b/docker/Dockerfile
@@ -1,4 +1,4 @@
-FROM ubuntu:focal AS stage_build
+FROM ubuntu:jammy AS stage_build
 
 ARG EMSCRIPTEN_VERSION=tot
 ENV EMSDK /emsdk
@@ -56,7 +56,7 @@
 # -------------------------------- STAGE DEPLOY --------------------------------
 # ------------------------------------------------------------------------------
 
-FROM ubuntu:focal AS stage_deploy
+FROM ubuntu:jammy AS stage_deploy
 
 COPY --from=stage_build /emsdk /emsdk
 
@@ -105,7 +105,7 @@
         build-essential \
         make \
         ant \
-        libidn11 \
+        libidn12 \
         cmake \
         openjdk-11-jre-headless \
     # Standard Cleanup on Debian images