Add user starred dashboards delete service

In order to make removal of unwnted metrics_user_starred_dashboards
available we need to add another service obejct to wrap that logic.

app/services/metrics/users_starred_dashboards/delete_service.rb

+# frozen_string_literal: true
+
+# Delete all matching Metrics::UsersStarredDashboard entries for given user based on matched dashboard_path, project
+module Metrics
+  module UsersStarredDashboards
+    class DeleteService < ::BaseService
+      def initialize(user, project, dashboard_path = nil)
+        @user, @project, @dashboard_path = user, project, dashboard_path
+      end
+
+      def execute
+        ServiceResponse.success(payload: { deleted_rows: starred_dashboards.delete_all })
+      end
+
+      private
+
+      attr_reader :user, :project, :dashboard_path
+
+      def starred_dashboards
+        # since deleted records are scoped to their owner there is no need to
+        # check if that user can delete them, also if user lost access to
+        # project it shouldn't block that user from removing them
+        dashboards = user.metrics_users_starred_dashboards
+
+        if dashboard_path.present?
+          dashboards.for_project_dashboard(project, dashboard_path)
+        else
+          dashboards.for_project(project)
+        end
+      end
+    end
+  end
+end

spec/services/metrics/users_starred_dashboards/delete_service_spec.rb

+# frozen_string_literal: true
+
+require 'spec_helper'
+
+describe Metrics::UsersStarredDashboards::DeleteService do
+  subject(:service_instance) { described_class.new(user, project, dashboard_path) }
+
+  let_it_be(:user) { create(:user) }
+  let_it_be(:project) { create(:project) }
+
+  describe '#execute' do
+    let_it_be(:user_starred_dashboard_1) { create(:metrics_users_starred_dashboard, user: user, project: project, dashboard_path: 'dashboard_1') }
+    let_it_be(:user_starred_dashboard_2) { create(:metrics_users_starred_dashboard, user: user, project: project) }
+    let_it_be(:other_user_starred_dashboard) { create(:metrics_users_starred_dashboard, project: project) }
+    let_it_be(:other_project_starred_dashboard) { create(:metrics_users_starred_dashboard, user: user) }
+
+    context 'without dashboard_path' do
+      let(:dashboard_path) { nil }
+
+      it 'does not scope user starred dashboards by dashboard path' do
+        result = service_instance.execute
+
+        expect(result.success?).to be_truthy
+        expect(result.payload[:deleted_rows]).to be(2)
+        expect(Metrics::UsersStarredDashboard.all).to contain_exactly(other_user_starred_dashboard, other_project_starred_dashboard)
+      end
+    end
+
+    context 'with dashboard_path' do
+      let(:dashboard_path) { 'dashboard_1' }
+
+      it 'does scope user starred dashboards by dashboard path' do
+        result = service_instance.execute
+
+        expect(result.success?).to be_truthy
+        expect(result.payload[:deleted_rows]).to be(1)
+        expect(Metrics::UsersStarredDashboard.all).to contain_exactly(user_starred_dashboard_2, other_user_starred_dashboard, other_project_starred_dashboard)
+      end
+    end
+  end
+end