Add linked items widget to Ticket work item type

What does this MR do and why?

The widget linked_items was missed when adding the new work item type Ticket so we need to add it in a separate migration.

Similarly to !128307 (merged), this MR adds a new entry to the work_item_widget_definitions table to define Linked items widget for the Ticket work item type.

DB review

Query plans

• Upsert widget definition: https://console.postgres.ai/gitlab/gitlab-production-tunnel-pg12/sessions/21772/commands/70628
• Rollback delete: https://console.postgres.ai/gitlab/gitlab-production-tunnel-pg12/sessions/21772/commands/70632

Migration output

UP

bin/rails db:migrate
main: == [advisory_lock_connection] object_id: 242360, pg_backend_pid: 36500
main: == 20230823140934 AddLinkedItemsWidgetToTicketWorkItemType: migrating =========
main: == 20230823140934 AddLinkedItemsWidgetToTicketWorkItemType: migrated (0.0240s)

main: == [advisory_lock_connection] object_id: 242360, pg_backend_pid: 36500
ci: == [advisory_lock_connection] object_id: 242620, pg_backend_pid: 36502
ci: == 20230823140934 AddLinkedItemsWidgetToTicketWorkItemType: migrating =========
ci: -- The migration is skipped since it modifies the schemas: [:gitlab_main].
ci: -- This database can only apply migrations in one of the following schemas: [:gitlab_ci, :gitlab_internal, :gitlab_shared].
ci: == 20230823140934 AddLinkedItemsWidgetToTicketWorkItemType: migrated (0.0062s)

ci: == [advisory_lock_connection] object_id: 242620, pg_backend_pid: 36502

DOWN

bin/rails db:migrate:down:main db:migrate:down:ci VERSION=20230823140934

main: == [advisory_lock_connection] object_id: 224860, pg_backend_pid: 12926
main: == 20230823140934 AddLinkedItemsWidgetToTicketWorkItemType: reverting =========
main: == 20230823140934 AddLinkedItemsWidgetToTicketWorkItemType: reverted (0.0257s)

main: == [advisory_lock_connection] object_id: 224860, pg_backend_pid: 12926
ci: == [advisory_lock_connection] object_id: 235020, pg_backend_pid: 13199
ci: == 20230823140934 AddLinkedItemsWidgetToTicketWorkItemType: reverting =========
ci: -- The migration is skipped since it modifies the schemas: [:gitlab_main].
ci: -- This database can only apply migrations in one of the following schemas: [:gitlab_ci, :gitlab_internal, :gitlab_shared].
ci: == 20230823140934 AddLinkedItemsWidgetToTicketWorkItemType: reverted (0.0086s)

ci: == [advisory_lock_connection] object_id: 235020, pg_backend_pid: 13199

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.

Related to #423058 (closed)