feat: add built-in Mercure support (#89)

* feat: Mercure support

* feat: add native Mercure support

* improvements

* feat: add Mercure UI

* fix: typo

* finish

Dockerfile

@@ -5,7 +5,7 @@
 
 # https://docs.docker.com/engine/reference/builder/#understand-how-arg-and-from-interact
 ARG PHP_VERSION=7.4
-ARG CADDY_VERSION=2.1.1
+ARG CADDY_VERSION=2
 
 # "php" stage
 FROM php:${PHP_VERSION}-fpm-alpine AS symfony_php
@@ -109,12 +109,16 @@ CMD ["php-fpm"]
 FROM caddy:${CADDY_VERSION}-builder-alpine AS symfony_caddy_builder
 
 RUN xcaddy build \
+    --with github.com/dunglas/mercure@main \
+    --with github.com/dunglas/mercure/caddy@main \
     --with github.com/dunglas/vulcain/caddy
 
 FROM caddy:${CADDY_VERSION} AS symfony_caddy
 
 WORKDIR /srv/app
 
+ENV MERCURE_DEMO="demo /srv/mercure-assets/"
+COPY --from=dunglas/mercure:v0.11 /srv/public /srv/mercure-assets/
 COPY --from=symfony_caddy_builder /usr/bin/caddy /usr/bin/caddy
 COPY --from=symfony_php /srv/app/public public/
 COPY docker/caddy/Caddyfile /etc/caddy/Caddyfile