Online backup of the galera database must desynchronize the node before backup

This fix aims to desynchonize the current node of the galera database to
avoid receiving any writes or syncs from the master node while the
backup is being performed, ensuring the consistency of the dump.

This procedure is specified on the product manual [1].

Not a clean cherry pick due to different naming of the role directory.

[1] https://galeracluster.com/library/training/tutorials/galera-backup.html

Closes-Bug: #1934654

Change-Id: I879abd53a17402a0860557d8e0e31ab0c560fcd4
(cherry picked from commit dea5ae0569)
(cherry picked from commit bf60d71718)
(cherry picked from commit 69a4efe4bf)

tripleo_ansible/roles/backup-and-restore/backup/tasks/db_backup.yml

@@ -101,6 +101,19 @@
   tags:
     - bar_create_recover_image
 
+- name: Galera desync the MySQL node
+  shell: |
+    set -o pipefail
+    {{ tripleo_container_cli }} exec {{ tripleo_backup_and_restore_mysql_container }} bash -c "mysql -p -u root \
+    -p{{ mysql_password.stdout }} --execute 'SET GLOBAL wsrep_desync = ON'"
+  when:
+    - mysql_password.stderr is defined
+    - enabled_galera
+    - tripleo_backup_and_restore_enable_snapshots|bool or not tripleo_backup_and_restore_service_manager|bool
+  tags:
+    - bar_create_recover_image
+  no_log: "{{ tripleo_backup_and_restore_hide_sensitive_logs | bool }}"
+
 - name: MySQL Grants backup
   shell: |
     set -o pipefail
@@ -127,6 +140,19 @@
     - bar_create_recover_image
   no_log: "{{ not ((ansible_verbosity | int) >= 2) | bool }}"
 
+- name: Galera sync the MySQL node
+  shell: |
+    set -o pipefail
+    {{ tripleo_container_cli }} exec {{ tripleo_backup_and_restore_mysql_container }} bash -c "mysql -p -u root \
+    -p{{ mysql_password.stdout }} --execute 'SET GLOBAL wsrep_desync = OFF'"
+  when:
+    - mysql_password.stderr is defined
+    - enabled_galera
+    - tripleo_backup_and_restore_enable_snapshots|bool or not tripleo_backup_and_restore_service_manager|bool
+  tags:
+    - bar_create_recover_image
+  no_log: "{{ tripleo_backup_and_restore_hide_sensitive_logs | bool }}"
+
 - name: Pause mysql.
   command: "{{ tripleo_container_cli }} pause {{ tripleo_backup_and_restore_mysql_container }}"
   when: