[v15] Add sortable notification cache variants

[rudream]

backport #39616 to branch/v15

Mostly clean backport, only change was adding this CheckAndSetDefaults check in newResourceWatcher, which is in master:

teleport/lib/services/watcher.go

Lines 126 to 129 in 2c1eb8d

	func newResourceWatcher(ctx context.Context, collector resourceCollector, cfg ResourceWatcherConfig) (*resourceWatcher, error) {
	if err := cfg.CheckAndSetDefaults(); err != nil {
	return nil, trace.Wrap(err)
	}