Please document "fake" ID for single tenancy Loki instances

Is your feature request related to a problem? Please describe. This feature request is to update the docs by explaining the relationship to the "fake" ID in Loki's Ruler. Please expand how to configure alerts in Loki using local storage in single tenancy mode.

Describe the solution you'd like The Ruler docs give examples of using local storage but do not explain the importance of the "fake" ID. The only mention is with respect to using the cortextool to query Loki. This implies the ID is specific to cortextool and not Loki. However, that's far from the truth as others have found out. The fake ID is part of the Ruler and is required to be included in the directory path for the alerts to work.

Consider this StackOverflow question asking why Loki is not alerting Alertmanager. The answer is because the directory and rule_path are missing /fake to indicate the instance ID.

Then there's this comment on issue #4654 with a link to Grafana Loki Multi-Tenancy. The comment clearly includes /fake in the local storage but not the rule_path.

Describe alternatives you've considered I've considered not trying to improve the documentation and moving on. Clearly that doesn't help others researching why Loki isn't sending alerts to Alertmanager when Loki is in single tenancy mode.

Additional context None.