cli: Register configuration option `store.max-look-back-period` as CLI argument (#4242)

* Register CLI flag for ChunkStoreConfig.MaxLookBackPeriod

Even though the flag is already deprecated, registering the flag is necessary
for generating the config reference documentation.

* Update pkg/storage/store.go

Co-authored-by: Owen Diehl <ow.diehl@gmail.com>

pkg/storage/store.go

@@ -83,6 +83,7 @@ type ChunkStoreConfig struct {
 // RegisterFlags adds the flags required to configure this flag set.
 func (cfg *ChunkStoreConfig) RegisterFlags(f *flag.FlagSet) {
 	cfg.StoreConfig.RegisterFlags(f)
+	f.Var(&cfg.MaxLookBackPeriod, "store.max-look-back-period", "This flag is deprecated. Use -querier.max-query-lookback instead.")
 }
 
 func (cfg *ChunkStoreConfig) Validate(logger log.Logger) error {