fix: enable plugins to implement the "caddyfile" patch

When nginx was removed in favour of caddy, we decided that plugin
implementations of the "caddyfile" patch should make use of the "port" local
variable. However, local variables are not available from inside plugin
patches, which are rendered outside of the context of the parent templates.

For a more extensive description of the problem, see:
overhangio/tutor-mfe#23 (comment)

We still want to make it easy for developers to decide what should the port be
for caddy hosts. To do so, we make use of environment variables that are passed
at runtime to the caddy container.

Thus, a regular plugin patch should look like this:

    {{ PLUGIN_HOST }}{$default_site_port} {
        import proxy "myplugin:8000"
    }

CHANGELOG-nightly.md

@@ -2,6 +2,7 @@
 
 Note: Breaking changes between versions are indicated by "💥".
 
+- [Bugfix] Make it possible for plugins to implement the "caddyfile" patch without relying on the "port" local variable.
 - 💥[Improvement] Move the Open edX forum to a [dedicated plugin](https://github.com/overhangio/tutor-forum/) (#450).
 - 💥[Improvement] Get rid of the "tutor-openedx" package, which is no longer supported.
 - [Bugfix] Fix running Caddy container in k8s, which should always be the case even if `ENABLE_WEB_PROXY` is false.

tutor/templates/apps/caddy/Caddyfile

@@ -25,14 +25,7 @@
     }
 }
 
-{% if ENABLE_HTTPS and ENABLE_WEB_PROXY %}
-{% set port = "" %}
-{# listening to https is disabled and we must only listen to http #}
-{% else %}
-{% set port = ":80" %}
-{% endif %}
-
-{{ LMS_HOST }}{{ port }}, {{ PREVIEW_LMS_HOST }}{{ port }} {
+{{ LMS_HOST }}{$default_site_port}, {{ PREVIEW_LMS_HOST }}{$default_site_port} {
     @favicon_matcher {
         path_regexp ^(.*)/favicon.ico$
     }
@@ -51,7 +44,7 @@
     {{ patch("caddyfile-lms")|indent(4) }}
 }
 
-{{ CMS_HOST }}{{ port }} {
+{{ CMS_HOST }}{$default_site_port} {
     @favicon_matcher {
         path_regexp ^(.*)/favicon.ico$
     }

tutor/templates/k8s/deployments.yml

@@ -17,6 +17,9 @@ spec:
       containers:
         - name: caddy
           image: {{ DOCKER_IMAGE_CADDY }}
+          env:
+          - name: default_site_port
+            value: "{% if not ENABLE_HTTPS or not ENABLE_WEB_PROXY %}:80{% endif %}"
           volumeMounts:
             - mountPath: /etc/caddy/
               name: config

tutor/templates/local/docker-compose.prod.yml

@@ -7,6 +7,8 @@ services:
     ports:
       - "{{ CADDY_HTTP_PORT }}:80"
       {% if ENABLE_HTTPS and ENABLE_WEB_PROXY %}- "443:443"{% endif %}
+    environment:
+      default_site_port: "{% if not ENABLE_HTTPS or not ENABLE_WEB_PROXY %}:80{% endif %}"
     volumes:
       - ../apps/caddy/Caddyfile:/etc/caddy/Caddyfile:ro
       {% if ENABLE_HTTPS and ENABLE_WEB_PROXY %}- ../../data/caddy:/data{% endif %}