Allow to supply multiline overrides to vendor_data

According to the documentation, it is expected to have a multiline data
inside vendor_data.json [1]

[1] https://cloudinit.readthedocs.io/en/latest/reference/datasources/openstack.html#vendor-data

Depends-On: https://review.opendev.org/c/openstack/ansible-config_template/+/924217
Closes-Bug: #2073171
Change-Id: Ifc1239e4ef768e94c44d8d07df7a0b93c73638f9

tasks/nova_post_install.yml

@@ -65,6 +65,7 @@
     mode: "0640"
     config_overrides: "{{ item.config_overrides }}"
     config_type: "{{ item.config_type }}"
+    yml_multilines: "{{ item.yml_multilines | default(omit) }}"
   with_items:
     - src: "nova.conf.j2"
       dest: "/etc/nova/nova.conf"
@@ -74,6 +75,7 @@
       dest: "/etc/nova/vendor_data.json"
       config_overrides: "{{ nova_vendor_data_overrides }}"
       config_type: "json"
+      yml_multilines: True
   notify:
     - Restart nova services
     - Restart uwsgi services