Update Dockerfiles and images for Spack v0.18.0 (#30216)

This PR updates the list of images we build nightly, deprecating 
Ubuntu 16.04 and CentOS 8 and adding Ubuntu 20.04, Ubuntu 22.04
and CentOS Stream. It also removes a lot of duplication by generating
the Dockerfiles during the CI workflow and uploading them as artifacts
for later inspection or reuse.

share/spack/templates/container/amazonlinux_2.dockerfile

@@ -14,11 +14,11 @@ RUN yum update -y \
         iproute \
         make \
         patch \
-        python \
-        python-pip \
-        python-setuptools \
+        python3 \
+        python3-pip \
+        python3-setuptools \
         unzip \
- && pip install boto3 \
+ && pip3 install boto3 \
  && rm -rf /var/cache/yum \
  && yum clean all
 {% endblock %}

share/spack/templates/container/centos_7.dockerfile

@@ -16,11 +16,11 @@ RUN yum update -y \
         iproute \
         make \
         patch \
-        python \
-        python-pip \
-        python-setuptools \
+        python3 \
+        python3-pip \
+        python3-setuptools \
         unzip \
- && pip install boto3 \
+ && pip3 install boto3 \
  && rm -rf /var/cache/yum \
  && yum clean all
 {% endblock %}

share/spack/templates/container/ubuntu_1604.dockerfile

@@ -1,32 +0,0 @@
-{% extends "container/bootstrap-base.dockerfile" %}
-{% block env_vars %}
-{{ super() }}
-ENV DEBIAN_FRONTEND=noninteractive   \
-    LANGUAGE=en_US.UTF-8 \
-    LANG=en_US.UTF-8 \
-    LC_ALL=en_US.UTF-8
-{% endblock %}
-{% block install_os_packages %}
-RUN apt-get -yqq update \
- && apt-get -yqq install --no-install-recommends \
-        build-essential \
-        ca-certificates \
-        curl \
-        file \
-        g++ \
-        gcc \
-        gfortran \
-        git \
-        gnupg2 \
-        iproute2 \
-        locales \
-        lua-posix \
-        make \
-        python3 \
-        python3-pip \
-        python3-setuptools \
-        unzip \
- && locale-gen en_US.UTF-8 \
- && pip3 install boto3 \
- && rm -rf /var/lib/apt/lists/*
-{% endblock %}

share/spack/templates/container/ubuntu_1804.dockerfile

@@ -1,6 +0,0 @@
-{% extends "container/ubuntu_1604.dockerfile" %}
-{% block post_checkout %}
-# [WORKAROUND]
-# https://bugs.launchpad.net/ubuntu/+source/lua-posix/+bug/1752082
-RUN ln -s posix_c.so /usr/lib/x86_64-linux-gnu/lua/5.2/posix.so
-{% endblock %}

share/spack/templates/container/ubuntu_1804.dockerfile

@@ -0,0 +1 @@
+ubuntu_2004.dockerfile

share/spack/templates/container/ubuntu_2004.dockerfile

@@ -1 +0,0 @@
-ubuntu_1604.dockerfile

share/spack/templates/container/ubuntu_2004.dockerfile

@@ -0,0 +1,32 @@
+{% extends "container/bootstrap-base.dockerfile" %}
+{% block env_vars %}
+{{ super() }}
+ENV DEBIAN_FRONTEND=noninteractive   \
+    LANGUAGE=en_US.UTF-8 \
+    LANG=en_US.UTF-8 \
+    LC_ALL=en_US.UTF-8
+{% endblock %}
+{% block install_os_packages %}
+RUN apt-get -yqq update \
+ && apt-get -yqq upgrade \
+ && apt-get -yqq install --no-install-recommends \
+        build-essential \
+        ca-certificates \
+        curl \
+        file \
+        g++ \
+        gcc \
+        gfortran \
+        git \
+        gnupg2 \
+        iproute2 \
+        locales \
+        make \
+        python3 \
+        python3-pip \
+        python3-setuptools \
+        unzip \
+ && locale-gen en_US.UTF-8 \
+ && pip3 install boto3 \
+ && rm -rf /var/lib/apt/lists/*
+{% endblock %}

share/spack/templates/container/ubuntu_2204.dockerfile

@@ -0,0 +1 @@
+ubuntu_2004.dockerfile