Scheme required for sitemap url CLI argument to pass validation

[wjh18]

Describe the bug
You can't enter your sitemap url via the cli without a URL scheme. Non-sitemap urls are converted successfully.

To Reproduce

$ psi example.com/sitemap.xml -f sitemap
> Invalid URL. Please enter a valid fully-qualified URL.
$ psi www.example.com/sitemap.xml -f sitemap
> Invalid URL. Please enter a valid fully-qualified URL.
$ psi www.example.com/sitemap.xml/ -f sitemap
> Invalid URL. Please enter a valid fully-qualified URL.

$ psi https://www.example.com/sitemap.xml/ -f sitemap
> Invalid sitemap URL provided. Please provide a URL to a valid XML sitemap.

Also, the last example is a separate issue caused by oversimplified extension validation where the trailing slash gets in the way. Might be worth taking a second look at that too.

Expected behavior
Should recognize as valid url where appropriate and add scheme if missing.

[wjh18]

Fixed in e0629ec

Issue wasn't just with sitemaps, it was any url args without a scheme that had either a path or filepath.