cli: Add support for listing and deleting Cell Broadcast messages

This adds

```
   $ mmcli -m 0 --cell-broadcast-list-cbm
       /org/freedesktop/ModemManager1/CBM/0 (received)
       /org/freedesktop/ModemManager1/CBM/0 (received)

   $ mmcli -m 0 --cell-broadcast-delete-cbm=0
   successfully deleted CBM from modem

   $ mmcli -m 0 --cbm 0
   --------------------------
   General    |         path: /org/freedesktop/ModemManager1/CBM/1
   --------------------------
   Content    |         text: This is a test of the Ontario Alert Ready System. There is no danger to your health or safety
   --------------------------
   Properties |       update: 0
              | message code: 0
```

Signed-off-by: Guido Günther <agx@sigxcpu.org>

cli/mmcli-cbm.c

@@ -0,0 +1,150 @@
+/* -*- Mode: C; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4 -*- */
+/*
+ * mmcli -- Control cbm information from the command line
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ *
+ * Copyright (C) 2024 Guido Günther <agx@sigxcpu.org>
+ */
+
+#include "config.h"
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <locale.h>
+#include <string.h>
+
+#include <glib.h>
+#include <gio/gio.h>
+
+#define _LIBMM_INSIDE_MMCLI
+#include <libmm-glib.h>
+
+#include "mmcli.h"
+#include "mmcli-common.h"
+#include "mmcli-output.h"
+
+/* Context */
+typedef struct {
+    MMManager *manager;
+    MMObject *object;
+    GCancellable *cancellable;
+    MMCbm *cbm;
+} Context;
+static Context *ctx;
+
+/* Options */
+static gboolean info_flag; /* set when no action found */
+
+static GOptionEntry entries[] = {
+    /* no options just info */
+    { NULL }
+};
+
+GOptionGroup *
+mmcli_cbm_get_option_group (void)
+{
+    GOptionGroup *group;
+
+    group = g_option_group_new ("cbm",
+                                "CBM options:",
+                                "Show CBM options",
+                                NULL,
+                                NULL);
+    g_option_group_add_entries (group, entries);
+
+    return group;
+}
+
+gboolean
+mmcli_cbm_options_enabled (void)
+{
+    static gboolean checked = FALSE;
+    int n_actions = 0;
+
+    if (checked)
+      return n_actions;
+
+    if (mmcli_get_common_cbm_string ()) {
+        /* default to info */
+        info_flag = TRUE;
+        n_actions++;
+    }
+
+    if (info_flag)
+        mmcli_force_sync_operation ();
+
+    checked = TRUE;
+    return !!n_actions;
+}
+
+static void
+context_free (void)
+{
+    if (!ctx)
+        return;
+
+    if (ctx->cancellable)
+        g_object_unref (ctx->cancellable);
+    if (ctx->cbm)
+        g_object_unref (ctx->cbm);
+    if (ctx->object)
+        g_object_unref (ctx->object);
+    if (ctx->manager)
+        g_object_unref (ctx->manager);
+    g_free (ctx);
+}
+
+void
+mmcli_cbm_shutdown (void)
+{
+    context_free ();
+}
+
+static void
+print_cbm_info (MMCbm *cbm)
+{
+    gchar *channel;
+    gchar *update;
+    gchar *code;
+
+    update = g_strdup_printf ("%u", mm_cbm_get_update (cbm));
+    channel = g_strdup_printf ("%u", mm_cbm_get_channel (cbm));
+    code = g_strdup_printf ("%u", mm_cbm_get_message_code (cbm));
+
+    mmcli_output_string           (MMC_F_CBM_GENERAL_DBUS_PATH,           mm_cbm_get_path (cbm));
+    mmcli_output_string           (MMC_F_CBM_CONTENT_TEXT,                mm_cbm_get_text (cbm));
+    mmcli_output_string_take      (MMC_F_CBM_PROPERTIES_CHANNEL,          channel);
+    mmcli_output_string_take      (MMC_F_CBM_PROPERTIES_UPDATE,           update);
+    mmcli_output_string_take      (MMC_F_CBM_PROPERTIES_MESSAGE_CODE,     code);
+
+    mmcli_output_dump ();
+}
+
+void
+mmcli_cbm_run_synchronous (GDBusConnection *connection)
+{
+    /* Initialize context */
+    ctx = g_new0 (Context, 1);
+    ctx->cbm = mmcli_get_cbm_sync (connection,
+                                   mmcli_get_common_cbm_string (),
+                                   &ctx->manager,
+                                   &ctx->object);
+
+    /* Setup operation timeout */
+    mmcli_force_operation_timeout (G_DBUS_PROXY (ctx->cbm));
+
+    g_debug ("Printing CBM info...");
+    print_cbm_info (ctx->cbm);
+}