data service: Add simple blue/green deployment to docker-compose.yml, add Caddyfiles to git

[RDMurray]

This duplicates the tilesrv service in docker-compose.yml, to allow for zero downtime updates of the tile server. tilesrv-blue is started by default.

• To update:

docker compose up --build -d tilesrv-green

• Test tilesrv-green on localhost:8082
• switch Caddy config:

  sudo ln -s /etc/caddy/Caddyfile.green /etc/caddy/Caddyfile
  sudo systemctl reload caddy

• if everything works, bring down tilesrv-blue:

  docker compose stop tilesrv-blue
  docker compose rm tilesrv-blue

This PR also restricts the 8081/8082 ports to localhost.

I chose 8081/8082 to make local testing easier since 8080 is a very common port.

This branch is already running on the production server.