cli: mark `rad fork` as obsolete — heartwood

The rad fork command was found to be confusing both in name and function. Rather than creating a hard fork of a repository, with a new identity, it pushes the default branch to the local user’s namespace.

This change modifies the copy of the help output, and marks the command as obsolete.

   config    Manage your local Radicle configuration
   debug     Write out information to help debug your Radicle node remotely
   follow    Manage node follow policies
   fork      Create a fork of a repository
   fork      [OBSOLETE] Copy the default branch of the repository under the current user's namespace
   id        Manage repository identities
   inbox     Manage your Radicle notifications
   init      Initialize a Radicle repository

 use radicle::rad;
 use crate::terminal as term;
 use crate::{terminal as term, warning};
 pub use args::Args;
 pub fn run(args: Args, ctx: impl term::Context) -> anyhow::Result<()> {
     warning::obsolete("rad fork");
     let profile = ctx.profile()?;
     let signer = profile.signer()?;
     let storage = &profile.storage;

 use radicle::identity::RepoId;
 const ABOUT: &str = "Create a fork of a repository";
 const ABOUT: &str =
     "[OBSOLETE] Copy the default branch of the repository under the current user's namespace";
 #[derive(Debug, clap::Parser)]
 #[command(about = ABOUT, disable_version_flag = true)]