fix(import-url): validate artifact URL scheme

[dipak0000812]

Description

Fixes #534

When import-url receives an artifact argument without an http:// or https:// prefix, parseImportURLArg previously returned the input unchanged and it was passed to mc.DownloadArtifact, resulting in a misleading server or connection error.

This change:

• Validates the artifact URL scheme in parseImportURLArg.
• Returns an errors.KindUsage error when the input does not start with http:// or https://.
• Propagates the validation error from import-url's RunE.
• Adds regression tests for relative paths, unsupported schemes (ftp://, file:///), empty input, and the reported issue syntax.

Testing

• go test -v ./cmd -run "TestImportURL|TestParseImportURLArg"
• go test ./...
• go vet ./...
• git diff --check

AI Assistance Disclosure

AI assistance was used minimally during development for codebase/policy lookup and review. The implementation, tests, and final verification were performed and reviewed by the author.

[github-actions]

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[Syedowais312]

LGTM, this matches what I proposed in #534. Thanks for picking it up, @dipak0000812

[lekaf974]

I think this way it gives to many responsibilities to this function.
Cobra offer pre-hook Args which is the right place for this kind of validation
this is also valid for the if len(arg) == 0 check

[Harsh4902]

Yes, I totally agree here. We can use that functionality to shift our validation much closer to the actual user input.

[dipak0000812]

Thanks for the feedback. I've updated the implementation:

• Moved missing-argument and URL-scheme validation into Cobra's Args validator.
• Validated all comma-separated URLs before RunE executes, preventing partial imports caused by invalid entries.
• Made scheme validation case-insensitive while preserving the original URL.
• Added regression tests for mixed-case schemes and upfront validation.

The targeted tests, go vet ./cmd/..., and git diff --check pass. I also verified that the full-suite Windows path-related failures reproduce on clean master.

I've pushed the changes in 2806c15. Thanks for the review.

[Syedowais312]

@dipak0000812 I think this validation can be removed from parseImportURLArg, since the Cobra Args validator already checks the URL scheme before RunE is called.

[dipak0000812]

Good point. I've removed the redundant scheme check from parseImportURLArg; URL scheme validation now happens in Cobra's Args validator, before RunE. The parser is focused on suffix parsing, and the existing regression tests pass. Pushed the update.