Add dashboard_path to PrometheusMetric

Adds dashboard_path to PrometheusMetric to support importing custom
metrics

changelogs/unreleased/rc-add_dashboard_path_to_prometheus_metrics.yml

+---
+title: Add dashboard_path to PrometheusMetric
+merge_request: 38237
+author:
+type: added

db/migrate/20200729175935_add_dashboard_path_to_prometheus_metrics.rb

+# frozen_string_literal: true
+
+class AddDashboardPathToPrometheusMetrics < ActiveRecord::Migration[6.0]
+  DOWNTIME = false
+
+  def up
+    # Text limit is added in 20200730210506_add_text_limit_to_dashboard_path
+    add_column :prometheus_metrics, :dashboard_path, :text # rubocop:disable Migration/AddLimitToTextColumns
+  end
+
+  def down
+    remove_column :prometheus_metrics, :dashboard_path
+  end
+end

db/migrate/20200730210506_add_text_limit_to_dashboard_path.rb

+# frozen_string_literal: true
+
+class AddTextLimitToDashboardPath < ActiveRecord::Migration[6.0]
+  include Gitlab::Database::MigrationHelpers
+
+  DOWNTIME = false
+
+  disable_ddl_transaction!
+
+  def up
+    add_text_limit(:prometheus_metrics, :dashboard_path, 2048)
+  end
+
+  def down
+    remove_text_limit(:prometheus_metrics, :dashboard_path)
+  end
+end

db/schema_migrations/20200729175935

+5f841d2032b55f01e944c50070a6bb102883c2e4da7ba155fdcf2e90f3b68707
\ No newline at end of file

db/schema_migrations/20200730210506

+85eb0a510cdb4b315aef1665f05ad3b93d5d39f4ddfe11ed5ddde63aa732f874
\ No newline at end of file

db/structure.sql

@@ -14657,7 +14657,9 @@ CREATE TABLE public.prometheus_metrics (
     created_at timestamp with time zone NOT NULL,
     updated_at timestamp with time zone NOT NULL,
     common boolean DEFAULT false NOT NULL,
-    identifier character varying
+    identifier character varying,
+    dashboard_path text,
+    CONSTRAINT check_0ad9f01463 CHECK ((char_length(dashboard_path) <= 2048))
 );
 
 CREATE SEQUENCE public.prometheus_metrics_id_seq

spec/lib/gitlab/import_export/safe_model_attributes.yml

@@ -659,6 +659,7 @@ PrometheusMetric:
 - group
 - common
 - identifier
+- dashboard_path
 PrometheusAlert:
 - threshold
 - operator