Fix license instrumented metrics

  - Fix licnese_id
  - Fix license_trial
  - Add tests

Fix Rubocop

ee/config/metrics/license/20210204124833_license_id.yml

@@ -12,7 +12,7 @@ data_source: license
 data_category: subscription
 instrumentation_class: LicenseMetric
 options:
-  attribute: id
+  attribute: license_id
 distribution:
 - ee
 tier:

ee/config/metrics/license/20210204124851_license_trial.yml

@@ -12,7 +12,7 @@ data_source: license
 data_category: subscription
 instrumentation_class: LicenseMetric
 options:
-  attribute: trial
+  attribute: 'trial?'
 distribution:
 - ee
 tier:

ee/lib/gitlab/usage/metrics/instrumentations/license_metric.rb

@@ -14,9 +14,9 @@ module Gitlab
           # end
 
           ALLOWED_ATTRIBUTES = %w(md5
-                                  id
+                                  license_id
                                   plan
-                                  trial
+                                  trial?
                                   starts_at
                                   expires_at
                                   user_count

ee/spec/lib/gitlab/usage/metrics/instrumentations/license_metric_spec.rb

+# frozen_string_literal: true
+
+require 'spec_helper'
+
+RSpec.describe Gitlab::Usage::Metrics::Instrumentations::LicenseMetric do
+  let(:current_license) { ::License.current }
+
+  it_behaves_like 'a correct instrumented metric value', { time_frame: 'none', options: { attribute: 'trial?' } } do
+    let(:expected_value) { current_license.trial? }
+  end
+
+  it_behaves_like 'a correct instrumented metric value', { time_frame: 'none', options: { attribute: 'license_id' } } do
+    let(:expected_value) { current_license.license_id }
+  end
+
+  it_behaves_like 'a correct instrumented metric value', { time_frame: 'none', options: { attribute: 'expires_at' } } do
+    let(:expected_value) { current_license.expires_at }
+  end
+
+  it_behaves_like 'a correct instrumented metric value', { time_frame: 'none', options: { attribute: 'md5' } } do
+    let(:expected_value) { current_license.md5 }
+  end
+
+  it_behaves_like 'a correct instrumented metric value', { time_frame: 'none', options: { attribute: 'trial_ends_on' } } do
+    let(:expected_value) { ::License.trial_ends_on }
+  end
+
+  it_behaves_like 'a correct instrumented metric value', { time_frame: 'none', options: { attribute: 'plan' } } do
+    let(:expected_value) { current_license.plan }
+  end
+
+  it_behaves_like 'a correct instrumented metric value', { time_frame: 'none', options: { attribute: 'subscription_id' } } do
+    let(:expected_value) { current_license.subscription_id }
+  end
+
+  it_behaves_like 'a correct instrumented metric value', { time_frame: 'none', options: { attribute: 'starts_at' } } do
+    let(:expected_value) { current_license.starts_at }
+  end
+
+  it_behaves_like 'a correct instrumented metric value', { time_frame: 'none', options: { attribute: 'user_count' } } do
+    let(:expected_value) { current_license.restricted_user_count }
+  end
+end