Add requeue workers setting

What does this MR do and why?

This MR adds a new setting to control advanced search indexing workers requeue. It will be false by default, but enabled on GitLab.com (current behaviour). We want to keep it disabled for self-managed customers because it has been causing problems for smaller instances by overloading their Sidekiq infrastructure.

Related to #415815 (closed)

Migrations

$ bin/rake db:migrate
main: == [advisory_lock_connection] object_id: 229060, pg_backend_pid: 79288
main: == 20230621065943 AddElasticsearchRequeueWorkersToApplicationSettings: migrating
main: -- add_column(:application_settings, :elasticsearch_requeue_workers, :boolean, {:null=>false, :default=>false})
main:    -> 0.0034s
main: == 20230621065943 AddElasticsearchRequeueWorkersToApplicationSettings: migrated (0.0076s)

main: == 20230621070810 UpdateRequeueWorkersInApplicationSettingsForGitlabCom: migrating
main: == 20230621070810 UpdateRequeueWorkersInApplicationSettingsForGitlabCom: migrated (0.0030s)

main: == [advisory_lock_connection] object_id: 229060, pg_backend_pid: 79288
ci: == [advisory_lock_connection] object_id: 229340, pg_backend_pid: 79418
ci: == [advisory_lock_connection] object_id: 229340, pg_backend_pid: 79418
embedding: == [advisory_lock_connection] object_id: 229440, pg_backend_pid: 79433
embedding: == [advisory_lock_connection] object_id: 229440, pg_backend_pid: 79433

$ bin/rake db:rollback:main STEP=2
main: == [advisory_lock_connection] object_id: 228760, pg_backend_pid: 87205
main: == 20230621070810 UpdateRequeueWorkersInApplicationSettingsForGitlabCom: reverting
main: == 20230621070810 UpdateRequeueWorkersInApplicationSettingsForGitlabCom: reverted (0.0033s)

main: == 20230621065943 AddElasticsearchRequeueWorkersToApplicationSettings: reverting
main: -- remove_column(:application_settings, :elasticsearch_requeue_workers, :boolean, {:null=>false, :default=>false})
main:    -> 0.0015s
main: == 20230621065943 AddElasticsearchRequeueWorkersToApplicationSettings: reverted (0.0053s)

main: == [advisory_lock_connection] object_id: 228760, pg_backend_pid: 87205

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