services/matrix: Automatically purge remote media

Remote media that has not been acessed in 90 days will be purged.
Sice purging remote media is currently doing enough to free up space,
I'd suggest not purging local media for now (thus setting the retention
to 10 years, thus virtually unlimited).

services/matrix/default.nix

@@ -89,7 +89,6 @@ in {
     static-auth-secret-file = config.sops.secrets."coturn_static_auth_secret".path;
   };
 
-  # TODO: Use media storage volume on prod
   services.matrix-synapse = {
     enable = true;
     plugins = [
@@ -147,6 +146,12 @@ in {
         user_mapping_provider.module = "matrix_synapse_saml_mapper.SamlMappingProvider";
       };
       password_config.enabled = false;
+      media_retention = {
+        # Since clearing remote media does the trick for now when it comes to purging old media
+        # keeping local media for virtually unlimited time (for now, may change in the future).
+        local_media_lifetime = "10y";
+        remote_media_lifetime = "90d";
+      };
     };
     extraConfigFiles = let
       format = (pkgs.formats.yaml {}).generate;