Allow editing redirects for domains not yet used in any short URL or new domains

[acelaya]

Summary

Currently, only the domains displayed in "Manage domains" allow editing the redirects.

Allow setting up redirects for new domains/domains not yet used on short URLs, as the REST API supports it, and it would match the behavior of the CLI command.

[acelaya]

Blocking this, as it has some considerations.

• Shlink only returns domains that have either been used for some short URL, or have some redirect explicitly configured. That means that "creating" a new domain with no redirects will make Shlink to not return it.
• Even if at least one redirect is enforced for "new domains", once created, you no longer know if the domain is used in some URL or not, so the user could edit it afterwards and remove the redirect/s.
  • This could be mitigated if Shlink returned the amount of URLs in which the domain is used.