Merge branch 'ab/schema-migration-timestamp' into 'master'

Track finished_at timestamp for schema migrations

See merge request gitlab-org/gitlab!64204

db/migrate/20210616134905_add_timestamp_to_schema_migration.rb

+# frozen_string_literal: true
+
+class AddTimestampToSchemaMigration < ActiveRecord::Migration[6.1]
+  def up
+    # Add a nullable column with default null first
+    add_column :schema_migrations, :finished_at, :timestamptz
+
+    # Change default to NOW() for new records
+    change_column_default :schema_migrations, :finished_at, -> { 'NOW()' }
+  end
+
+  def down
+    remove_column :schema_migrations, :finished_at
+  end
+end

db/schema_migrations/20210616134905

+52843d12ab18b92c71a334cf877682d9fae57632cf0ba14213dfc0543e39cf1b
\ No newline at end of file

db/structure.sql

@@ -17715,7 +17715,8 @@ CREATE SEQUENCE saml_providers_id_seq
 ALTER SEQUENCE saml_providers_id_seq OWNED BY saml_providers.id;
 
 CREATE TABLE schema_migrations (
-    version character varying NOT NULL
+    version character varying NOT NULL,
+    finished_at timestamp with time zone DEFAULT now()
 );
 
 CREATE TABLE scim_identities (