Docker compose config for demo CTFE

[mhutchinson]

The previous instructions have rotted and no longer work. This aims to fill in the gap of a HelloWorld deployment for CTFE. This is explicitly NOT a guide on how to deploy this in a production setting. This is a docker version of the updated instructions from #1061

[roger2hk]

In my codespaces instance, the generated Docker container name of the database is ctfe-db-1 instead of ctfe_db_1.

➜ /workspaces/trillian (master) $ docker container ls
CONTAINER ID   IMAGE                                      COMMAND                  CREATED         STATUS                   PORTS                                                           NAMES
438dbabdde36   gcr.io/trillian-opensource-ci/log_signer   "/trillian_log_signe…"   7 minutes ago   Up 6 minutes             0.0.0.0:8092->8091/tcp, :::8092->8091/tcp                       ctfe-trillian-log-signer-1
7ffdd2b307da   gcr.io/trillian-opensource-ci/log_server   "/trillian_log_serve…"   7 minutes ago   Up 6 minutes             0.0.0.0:8090-8091->8090-8091/tcp, :::8090-8091->8090-8091/tcp   ctfe-trillian-log-server-1
d4e1fb3a39f4   mariadb                                    "docker-entrypoint.s…"   7 minutes ago   Up 7 minutes (healthy)   0.0.0.0:3306->3306/tcp, :::3306->3306/tcp                       ctfe-db-1