Added palette contract

Necessary to validate the Palette API response. I've logged and issue against our Core project to improve upon this further since the API design is inconsistent so hoping this will improve soon.

Milestone: minor

lib/trmnl/api/container.rb

@@ -26,6 +26,7 @@ module TRMNL
         register :firmware, Contracts::Firmware
         register :ip_address, Contracts::IPAddress
         register :model, Contracts::Model
+        register :palette, Contracts::Palette
         register :setup, Contracts::Setup
       end
 

lib/trmnl/api/contracts/palette.rb

@@ -0,0 +1,20 @@
+# frozen_string_literal: true
+
+require "dry/schema"
+
+module TRMNL
+  module API
+    module Contracts
+      # Validates API response.
+      Palette = Dry::Schema.JSON do
+        required(:data).array(:hash) do
+          required(:id).filled :string
+          required(:name).filled :string
+          optional(:grays).maybe :integer
+          optional(:colors).maybe(:array)
+          optional(:framework_class).maybe :string
+        end
+      end
+    end
+  end
+end