Document the common config section (#4485)
Document the common config section (#4485)

* Document the common_config section.

* Apply suggestions from code review

Fix subsection reference from `filesystem_storage_config` to `local_storage_config`

Co-authored-by: Owen Diehl <b7f53a77a4950cb4aa47d9da3f442809e803fde5@gmail.com>

Co-authored-by: Owen Diehl <b7f53a77a4950cb4aa47d9da3f442809e803fde5@gmail.com>
grafana/loki,grafana/loki,grafana/loki,grafana/loki,grafana/loki,grafana/loki