cli: suggest "jj git init" if workspace looks like a plain git repo

cli/src/cli_util.rs

@@ -1882,7 +1882,7 @@ fn map_workspace_load_error(err: WorkspaceLoadError, workspace_path: Option<&str
                     message,
                     "It looks like this is a git repo. You can create a jj repo backed by it by \
                      running this:
-jj init --git-repo=.",
+jj git init --git-repo=.",
                 )
             } else {
                 user_error(message)

cli/tests/test_global_opts.rs

@@ -210,7 +210,7 @@ fn test_no_workspace_directory() {
     insta::assert_snapshot!(stderr, @r###"
     Error: There is no jj repo in "."
     Hint: It looks like this is a git repo. You can create a jj repo backed by it by running this:
-    jj init --git-repo=.
+    jj git init --git-repo=.
     "###);
 }