mysql_user, mysql_role: add argument subtract_privs to revoke privileges explicitly (#333)

* add option subtract_privs to mysql_role and mysql_user

see https://github.com/ansible-collections/community.mysql/issues/331

* add integration tests for subtract_privs for mysql_role and mysql_user

* add changelog fragment for PR #333

* mysql_role, mysql_user: when subtract_privileges, don't grant unwanted privileges and don't revoke USAGE implicitly

* fix integration tests

* mysql_role, mysql_user: invalid privileges are ignored when subtract_privs is true -> document that and fix integration tests

* fix mysql_role integration tests

* fix mysql_role, mysql_user integration tests

* formatting

make the PEP8 check happy

* mysql_user and mysql_role: fix granting privileges when only the GRANT OPTION needs to be added

* mysql_user and mysql_role: log some updated privileges; explain integration test blind spot

* mysql_user and mysql_role: don't grant too much privileges

If only the grant option needs to be granted, at least one privilege needs to be granted to get valid syntax. USAGE is better for that than the existing privileges, because unwanted privileges would be re-added after revokation.

* mysql_user and mysql_role: fix type error

* Update changelogs/fragments/333-mysql_user-mysql_role-add-subtract_privileges-argument.yml

Co-authored-by: Andrew Klychkov <aaklychkov@mail.ru>

* Update plugins/modules/mysql_role.py

Co-authored-by: Andrew Klychkov <aaklychkov@mail.ru>

* Update plugins/modules/mysql_user.py

Co-authored-by: Andrew Klychkov <aaklychkov@mail.ru>

Co-authored-by: Felix Hamme <felix.hamme@ionos.com>
Co-authored-by: Andrew Klychkov <aaklychkov@mail.ru>

tests/integration/targets/test_mysql_role/defaults/main.yml

@@ -14,3 +14,4 @@ nonexistent: user3
 
 role0: role0
 role1: role1
+role2: role2