Add key- and valuePlaceholders for quarantined_instances and mrf_simple

* I also added for keywordpolicy as well now. It was done in the admin-fe, but is better to be done here
* I also added comments to explain why we did the _info keys (backwards compatibility)

config/description.exs

@@ -688,6 +688,8 @@
       %{
         key: :quarantined_instances,
         type: {:list, :tuple},
+        keyPlaceholder: "instance",
+        valuePlaceholder: "reason",
         description:
           "List of ActivityPub instances where private (DMs, followers-only) activities will not be sent and the reason for doing so",
         suggestions: [

lib/pleroma/web/activity_pub/mrf/keyword_policy.ex

@@ -159,6 +159,8 @@ def config_description do
         %{
           key: :replace,
           type: {:list, :tuple},
+          keyPlaceholder: "pattern",
+          valuePlaceholder: "replacement",
           description: """
             **Pattern**: a string or [Regex](https://hexdocs.pm/elixir/Regex.html) in the format of `~r/PATTERN/`.
 

lib/pleroma/web/activity_pub/mrf/simple_policy.ex

@@ -271,6 +271,10 @@ def describe do
       end)
       |> Enum.into(%{})
 
+    # This is for backwards compatibility. We originally didn't sent
+    # extra info like a reason why an instance was rejected/quarantined/etc.
+    # Because we didn't want to break backwards compatibility it was decided
+    # to add an extra "info" key.
     mrf_simple_info =
       mrf_simple_excluded
       |> Enum.map(fn {k, v} -> {k, Enum.reject(v, fn {_, reason} -> reason == "" end)} end)

lib/pleroma/web/mastodon_api/views/instance_view.ex

@@ -100,6 +100,10 @@ def federation do
           quarantined
           |> Enum.map(fn {instance, _reason} -> instance end)
       })
+      # This is for backwards compatibility. We originally didn't sent
+      # extra info like a reason why an instance was rejected/quarantined/etc.
+      # Because we didn't want to break backwards compatibility it was decided
+      # to add an extra "info" key.
       |> Map.merge(%{
         quarantined_instances_info: %{
           "quarantined_instances" =>