`-list-targets` should not require a config file

[chaudum]

Describe the bug
Running loki -list-targets prints and exits with exit code 1.

failed parsing config: config.yaml,config/config.yaml does not exist, set config.file for custom config path

A clear and concise description of what the bug is.

To Reproduce
Steps to reproduce the behavior:

1. Run loki -list-targets

Expected behavior
The output shows all targets as when run loki -config.file=loki.yaml -list-targets.

[pinkbit256]

Hi, @chaudum I’d like to work on this issue. Do you mind if I take this one?