Currently deno add only works with jsr: and npm: specifiers.
We should add an ability to do deno add https://deno.land/x/foo/bar.ts.
To do this, we should leverage existing infer_name_from_url() helper, that is already used in deno install and deno compile
https://github.com/denoland/deno/blob/d3d3582b1f1b71b18d8d89cdf8e14f112b8f40a7/cli/tools/installer.rs#L131-L185