feat: Add APIs for custom attribute definitions (#2689)

app/controllers/api/v1/accounts/custom_attribute_definitions_controller.rb

@@ -0,0 +1,50 @@
+class Api::V1::Accounts::CustomAttributeDefinitionsController < Api::V1::Accounts::BaseController
+  before_action :fetch_custom_attributes_definitions, except: [:create]
+  before_action :fetch_custom_attribute_definition, only: [:show, :update, :destroy]
+  DEFAULT_ATTRIBUTE_MODEL = 'conversation_attribute'.freeze
+
+  def index; end
+
+  def show; end
+
+  def create
+    @custom_attribute_definition = Current.account.custom_attribute_definitions.create!(
+      permitted_payload
+    )
+  end
+
+  def update
+    @custom_attribute_definition.update!(permitted_payload)
+  end
+
+  def destroy
+    @custom_attribute_definition.destroy
+    head :no_content
+  end
+
+  private
+
+  def fetch_custom_attributes_definitions
+    @custom_attribute_definitions = Current.account.custom_attribute_definitions.where(
+      attribute_model: permitted_params[:attribute_model] || DEFAULT_ATTRIBUTE_MODEL
+    )
+  end
+
+  def fetch_custom_attribute_definition
+    @custom_attribute_definition = @custom_attribute_definitions.find(permitted_params[:id])
+  end
+
+  def permitted_payload
+    params.require(:custom_attribute_definition).permit(
+      :attribute_display_name,
+      :attribute_display_type,
+      :attribute_key,
+      :attribute_model,
+      :default_value
+    )
+  end
+
+  def permitted_params
+    params.permit(:id, :filter_type)
+  end
+end