Loki logs errors non-existing directory before it is created

[aslafy-z]

Describe the bug
See grafana/mimir#1058
The issue is the same with the rule_path ruler directory.

To Reproduce
Steps to reproduce the behavior:

1. Started Loki (v2.5.0) with ruler enabled

Expected behavior
It should not log that error since loki creates the folder few seconds after.

Screenshots, Promtail config, or terminal output

level=error ts=2022-05-02T10:10:03.156433457Z caller=mapper.go:50 msg="unable to read rules directory" path=/tmp/loki/scratch err="open /tmp/loki/scratch: no such file or directory"