Add tls label (alias of tls-email)

[HugoDF]

Closes #18

• adds a tls label (that gets injected as the tls value if tls-email is not set)
• update the docs

How to test:

Build container:

docker build -t caddy-gen-dev .

Create empty directory and have a docker-compose.yml file:

version: "3"
services:
  caddy-gen:
    container_name: caddy-gen
    image: "caddy-gen-dev:latest" # IMPORTANT
    restart: always
    volumes:
      - /var/run/docker.sock:/tmp/docker.sock:ro  # needs socket to read events
      - ./certs/acme:/etc/caddy/acme  # to save acme
      - ./certs/ocsp:/etc/caddy/ocsp  # to save certificates
    ports:
      - "80:80"
      - "443:443"
    depends_on:
      - whoami

  whoami:  # this is your service
    image: "katacoda/docker-http-server:v2"
    labels:
      - "virtual.host=myapp.com"  # your domain
      - "virtual.port=80"  # exposed port of this container
      - "virtual.tls=admin@myapp.com"  # ssl is now on

Run:

docker-compose up

Output:

Creating test-caddy-gen-patch_whoami_1 ... done
Creating caddy-gen                     ... done
whoami_1     | Web Server started. Listening on 0.0.0.0:80
caddy-gen    | 2019/03/10 19:02:33 Generated '/etc/caddy/Caddyfile' from 2 containers
caddy-gen    | forego     | starting dockergen.1 on port 5000
caddy-gen    | forego     | starting caddy.1 on port 5100
caddy-gen    | dockergen.1 | 2019/03/10 19:02:33 Contents of /etc/caddy/Caddyfile did not change. Skipping notification ''
caddy-gen    | dockergen.1 | 2019/03/10 19:02:33 Watching docker events
caddy-gen    | dockergen.1 | 2019/03/10 19:02:34 Contents of /etc/caddy/Caddyfile did not change. Skipping notification ''
caddy-gen    | caddy.1    | Activating privacy features... 2019/03/10 19:02:34 [INFO] acme: Registering account for admin@myapp.com

Caddy attempted to create certificates with admin@myapp.com, which means virtual.tls gets injected as the tls directive value.

Alternatively, could attempt to use https://github.com/HugoDF/docker-compose-local-https/tree/master/caddy-gen, switch out the image at https://github.com/HugoDF/docker-compose-local-https/blob/master/caddy-gen/docker-compose.yml#L4 for caddy-gen-dev:latest and switch virtual.tls-email for virtual.tls.

[sobolevn]

Thanks!