Implement public actor ICS endpoint and event ICS export

Closes #83 and #84

Signed-off-by: Thomas Citharel <tcit@tcit.fr>

lib/mobilizon/application.ex

@@ -4,6 +4,7 @@ defmodule Mobilizon.Application do
   """
   use Application
   import Cachex.Spec
+  alias Mobilizon.Service.Export.{Feed, ICalendar}
 
   # See https://hexdocs.pm/elixir/Application.html
   # for more information on OTP Applications
@@ -29,11 +30,27 @@ defmodule Mobilizon.Application do
                 default: :timer.minutes(60),
                 interval: :timer.seconds(60)
               ),
-            fallback: fallback(default: &Mobilizon.Service.Feed.create_cache/1)
+            fallback: fallback(default: &Feed.create_cache/1)
           ]
         ],
         id: :cache_feed
       ),
+      worker(
+        Cachex,
+        [
+          :ics,
+          [
+            limit: 2500,
+            expiration:
+              expiration(
+                default: :timer.minutes(60),
+                interval: :timer.seconds(60)
+              ),
+            fallback: fallback(default: &ICalendar.create_cache/1)
+          ]
+        ],
+        id: :cache_ics
+      ),
       worker(
         Cachex,
         [