Docker builds are stale/nonfunctional

[coandco]

The package repository for CentOS 8 has been shut down, so the current Dockerfiles are nonfunctional, as seen here:

$ docker build -f Dockerfile.server -t test .
Sending build context to Docker daemon  9.216kB
Step 1/12 : FROM centos:8 as base
 ---> 5d0da3dc9764
Step 2/12 : ENV BUILD_REPOS="epel-release centos-release-scl"     BUILD_DEPS="cmake3 boost-devel libsodium-devel protobuf-devel     protobuf-compiler gflags-devel protobuf-lite-devel git     perl-IPC-Cmd perl-Data-Dumper libunwind-devel libutempter-devel     devtoolset-11 devtoolset-11-libatomic-devel rh-git227"
 ---> Using cache
 ---> ae886d2be74a
Step 3/12 : WORKDIR /
 ---> Using cache
 ---> 6173c9c68d7f
Step 4/12 : RUN yum install -y $BUILD_REPOS &&     yum install -y $BUILD_DEPS &&     git clone --recurse-submodules https://github.com/MisterTea/EternalTerminal.git &&     cd EternalTerminal &&     mkdir build &&     cd build &&     bash -c "scl enable devtoolset-11 rh-git227 'cmake3 ../'" &&     bash -c "scl enable devtoolset-11 'make -j $(grep ^processor /proc/cpuinfo |wc -l) && make install'"
 ---> Running in cf2a9bd56d9b
CentOS Linux 8 - AppStream                      0.0  B/s |   0  B     00:00
Errors during downloading metadata for repository 'appstream':
  - Curl error (6): Couldn't resolve host name for http://mirrorlist.centos.org/?release=8&arch=x86_64&repo=AppStream&infra=container [Could not resolve host: mirrorlist.centos.org]
Error: Failed to download metadata for repo 'appstream': Cannot prepare internal mirrorlist: Curl error (6): Couldn't resolve host name for http://mirrorlist.centos.org/?release=8&arch=x86_64&repo=AppStream&infra=container [Could not resolve host: mirrorlist.centos.org]
The command '/bin/sh -c yum install -y $BUILD_REPOS &&     yum install -y $BUILD_DEPS &&     git clone --recurse-submodules https://github.com/MisterTea/EternalTerminal.git &&     cd EternalTerminal &&     mkdir build &&     cd build &&     bash -c "scl enable devtoolset-11 rh-git227 'cmake3 ../'" &&     bash -c "scl enable devtoolset-11 'make -j $(grep ^processor /proc/cpuinfo |wc -l) && make install'"' returned a non-zero code: 1

I've made PR #658 to address this and update the base OS to a modern distribution.

[coandco]

If you'd rather stick with a redhat-based distro, I have a branch that uses RockyLinux as well, using the EPEL version of the package here.