Fix mysql_user on_new_username IndexError (#642)

* fix tuple indexerror when no accounts are found

* Fix tests for update_password not executed

* Add test for case where existing user have different password

* lint to prevent warning about jinja templating in when clause

* Refactor get_existing_authentication to return a list of all row found

Previously we were returning only the first row found. We need to be
able to see if there is a difference in the existing passwords.

* Refactor host option to be optional

This make it possible to use the same method from mysql_user to help
update_password retrieve existing password for all account with the same
username independently of their hostname. And from mysql_info to get
the password of a specif user using WHERE user = '' AND host = ''

* Add change log fragment

* Add link to the PR in the change log

* lint for ansible devel

* Fix templating type error could not cconvert to bool with ansible devel

* Revert changes made for ansible-devel that broke tests for Ansible 2.15

* Revert changes made for ansible-devel that broke tests

* Cut unnecessary set, uniqueness is ensured by the group_by in the query

* Cut auth plugin from returned values when multiple existing auths exists

Discussed here:
https://github.com/ansible-collections/community.mysql/pull/642/files#r1649720519

* fix convertion of list(dict) to list(tuple)

* Fix test for empty password on MySQL 8+

tests/integration/targets/test_mysql_user/tasks/main.yml

@@ -295,3 +295,7 @@
     - name: Mysql_user - test column case sensitive
       ansible.builtin.import_tasks:
         file: test_column_case_sensitive.yml
+
+    - name: Mysql_user - test update_password
+      ansible.builtin.import_tasks:
+        file: test_update_password.yml