cli: Make sure to configure checkouts properly

We were configure correctly on `rad init`, but not `rad checkout`.

radicle-cli/examples/rad-checkout-repo-config-linux.md

@@ -11,6 +11,8 @@ $ cat .git/config
 	repositoryformatversion = 0
 	filemode = true
 	logallrefupdates = true
+[push]
+	default = upstream
 [remote "rad"]
 	url = rad://z42hL2jL4XNk6K8oHQaSWfMgCL7ji
 	fetch = +refs/heads/*:refs/remotes/rad/*

radicle-cli/examples/rad-checkout-repo-config-macos.md

@@ -13,6 +13,8 @@ $ cat .git/config
 	ignorecase = true
 	precomposeunicode = true
 	logallrefupdates = true
+[push]
+	default = upstream
 [remote "rad"]
 	url = rad://z42hL2jL4XNk6K8oHQaSWfMgCL7ji
 	fetch = +refs/heads/*:refs/remotes/rad/*

radicle/src/rad.rs

@@ -222,6 +222,8 @@ pub fn checkout<P: AsRef<Path>, S: storage::ReadStorage>(
     let repo = git2::Repository::init_opts(path.as_ref(), &opts)?;
     let url = git::Url::from(proj);
 
+    // Configure repository for radicle.
+    git::configure_repository(&repo)?;
     // Configure and fetch all refs from remote.
     git::configure_remote(
         &repo,