cli: reject `rad id` proposals that do not verify

To ensure that the `rad id` command does not modify the project payload without
it being able to be deserialized into the `Project` type, the command performs
this check throught the `project` method, and returns an error if this fails.

Signed-off-by: Fintan Halpenny <fintan.halpenny@gmail.com>
X-Clacks-Overhead: GNU Terry Pratchett

radicle-cli/examples/rad-id-update-delete-field.md

@@ -69,3 +69,10 @@ $ rad id update --title "Delete field" --description "Delete 'web'" --payload xy
    "threshold": 1
  }
 ```
+
+Note that we cannot delete mandatory fields:
+
+``` (fails)
+$ rad id update --title "Delete default branch" --payload xyz.radicle.project defaultBranch null
+✗ Error: failed to verify `xyz.radicle.project`, failed with json: missing field `defaultBranch`
+```

radicle-cli/src/commands/id.rs

@@ -390,6 +390,11 @@ pub fn run(options: Options, ctx: impl term::Context) -> anyhow::Result<()> {
                         anyhow::bail!("payload `{id}` not found in identity document");
                     }
                 }
+                // Verify that the project payload can still be parsed into the
+                // `Project` type.
+                if let Err(e) = proposal.project() {
+                    anyhow::bail!("failed to verify `xyz.radicle.project`, failed with {e}",);
+                }
                 proposal
             };
             if proposal == current.doc {