feat(pm): support ‎http(s): specifiers and aliases for ‎deno add

[kingsword09]

This PR implements two related features for the ‎deno add command as described in #23216  and #23144 :

• Adds support for ‎http: and ‎https: specifiers, allowing users to do
  deno add path@https://deno.land/std/path/mod.ts fs@https://deno.land/std/fs/mod.ts

[CLAassistant]

All committers have signed the CLA.

[Hajime-san]

Could we trust connecting to a registry without TLS except for localhost?

[anonhostpi]

Could we trust connecting to a registry without TLS except for localhost?

Yes and no. In some applications, TLS adds unnecessary overhead in environments that don't require secure comm (isolated networks are a common example).

It should be up to the end user to decide if they want to make themselves vulnerable to MitM attacks.

What I would recommend is warning the user that the usage of http makes them susceptible to malicious code injection via MitM