Update docker implementation

I've made various updates to the docker implementation to work with the
latest php7 and currently blocks php8 until we deem nntmux ready. I've
also made modifications that allow for customizations without leaving a
dirty git status i.e. moving redis, etc. to an overrides file that is
gitignored and php customizations i.e. locale to a local overrides file
that is also gitignored.

The new docker implementation utilizes supervisord to run various
services in the web container, i.e. nginx, php-fpm, horizon, etc.

I plan to continue to maintain this as needed. Closes #1152

docker/supervisor.d/horizon.ini

@@ -0,0 +1,11 @@
+[program:horizon]
+command=php /site/artisan horizon
+autostart=true
+autorestart=true
+priority=5
+stdout_logfile=/dev/stdout
+stdout_events_enabled=true
+stdout_logfile_maxbytes=0
+stderr_logfile=/dev/stderr
+stderr_events_enabled=true
+stderr_logfile_maxbytes=0