* dvc cli: fixed error in 'dvc config --list' in non repo dir
Fixes#6496
* Issue 6496: Added test that covers the issue
* dvc cli: fixes error in 'dvc config <name>' in non dvc repo dir
Fixes the specified error. Did some refactoring based on previous commits.
Also added a test case for setting config in non dvc repo dir.
Fixes#6496
* Issue-6496: dvc config --<level> and dvc config --list --<level> will now throw config error if ran in non dvc repo with repo only level
* Issue 6496: Segregated config levels into repo and system levels that helped in simplifying the logic to decide appropriate level at the time of cli operation.