Add index for cluster_id in vulnerability_occurrences location

This change adds GIN index on location->cluster_id
in vulnerability_occurrences table. location is a jsonb column
and cluster_id field will only be present for
cluster_image_scanning report_type.

Changelog: performance

db/post_migrate/20211022112202_add_cluster_id_location_index_to_vulnerability_occurrences.rb

+# frozen_string_literal: true
+
+class AddClusterIdLocationIndexToVulnerabilityOccurrences < Gitlab::Database::Migration[1.0]
+  disable_ddl_transaction!
+
+  INDEX_NAME = 'index_vulnerability_occurrences_on_location_cluster_id'
+
+  def up
+    add_concurrent_index :vulnerability_occurrences, "(location -> 'cluster_id')",
+                         using: 'GIN',
+                         where: 'report_type = 7',
+                         name: INDEX_NAME
+  end
+
+  def down
+    remove_concurrent_index_by_name :vulnerability_occurrences, INDEX_NAME
+  end
+end

db/schema_migrations/20211022112202

+b5fbbfe186b3eeeb88bfd901ac426fc52355b71b67c5f5b42373008c19c35bee
\ No newline at end of file

db/structure.sql

@@ -27063,6 +27063,8 @@ CREATE INDEX index_vulnerability_occurrences_deduplication ON vulnerability_occu
 
 CREATE INDEX index_vulnerability_occurrences_for_issue_links_migration ON vulnerability_occurrences USING btree (project_id, report_type, encode(project_fingerprint, 'hex'::text));
 
+CREATE INDEX index_vulnerability_occurrences_on_location_cluster_id ON vulnerability_occurrences USING gin (((location -> 'cluster_id'::text))) WHERE (report_type = 7);
+
 CREATE INDEX index_vulnerability_occurrences_on_location_image ON vulnerability_occurrences USING gin (((location -> 'image'::text))) WHERE (report_type = ANY (ARRAY[2, 7]));
 
 CREATE INDEX index_vulnerability_occurrences_on_primary_identifier_id ON vulnerability_occurrences USING btree (primary_identifier_id);