cli: add check config flag

[MarcelCoding]

What kind of change does this PR introduce? (check at least one)

• [ ] Bugfix
• [x] Feature
• [ ] Code style update
• [ ] Refactor
• [ ] Build-related changes
• [ ] Other, please describe:

The PR fulfills these requirements:

• [ ] All tests are passing?
• [ ] New/updated tests are included?
• [ ] If any static assets have been updated, has ui/bindata.go been regenerated?
• [ ] Are there doc blocks for functions that I updated/created?

If adding a new feature, the PR's description includes:

• [x] A convincing reason for adding this feature (to avoid wasting your time, it's best to open a suggestion issue first and wait for approval before working on it)

Reason: Validate Configuration files in e.g. NixOS. https://github.com/NixOS/nixpkgs/pull/322508

Other information: