Add index for vulnerability_occurrences image location

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

Changelog: performance

db/post_migrate/20210921062820_add_image_location_index_to_vulnerability_occurrences.rb

+# frozen_string_literal: true
+
+class AddImageLocationIndexToVulnerabilityOccurrences < Gitlab::Database::Migration[1.0]
+  disable_ddl_transaction!
+
+  INDEX_NAME = 'index_vulnerability_occurrences_on_location_image'
+
+  def up
+    add_concurrent_index :vulnerability_occurrences, "(location -> 'image')",
+                         using: 'GIN',
+                         where: 'report_type IN (2, 7)',
+                         name: INDEX_NAME
+  end
+
+  def down
+    remove_concurrent_index_by_name :vulnerability_occurrences, INDEX_NAME
+  end
+end

db/schema_migrations/20210921062820

+ae98a673b649faf8644990de328470579e121544d4fc417562cc64a7687550ca
\ No newline at end of file

db/structure.sql

@@ -26809,6 +26809,8 @@ 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_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);
 
 CREATE INDEX index_vulnerability_occurrences_on_project_fingerprint ON vulnerability_occurrences USING btree (project_fingerprint);