Adds replication_factor doc to common config (#4683)

Oops, looks like we missed adding this to the configuration docs.

docs/sources/configuration/_index.md

@@ -2315,6 +2315,9 @@ This way, one doesn't have to replicate configs in multiple places.
 # When defined, the given prefix will be present in front of the endpoint paths.
 [path_prefix: <string>]
 
+# How many times incoming data should be replicated to the ingester component.
+[replication_factor: <int> | default = 3]
+
 # When true, the ingester, compactor and query_scheduler ring tokens will be saved to files in the path_prefix directory
 # Loki will error if you set this to true and path_prefix is empty.
 [persist_tokens: <boolean>: default = false]