Bug #93348 Always log the use of group_replication_allow_local_disjoint_gtids_join

Description:
group_replication_allow_local_disjoint_gtids_join, which is deprecated, when used a log message should always be logged.
Currently its use is logged when GR starts automatically on server start, but it is not when GR is started by START GROUP_REPLICATION.

```
 285 static void option_deprecation_warning(MYSQL_THD thd, const char* name)
 286 {
 287   if (thd != NULL)
 288   {
 289     push_warning_printf(thd, Sql_condition::SL_WARNING,
 290                         ER_WARN_DEPRECATED_SYNTAX_NO_REPLACEMENT,
 291                         ER_THD(thd, ER_WARN_DEPRECATED_SYNTAX_NO_REPLACEMENT),
 292                         name);
 293   }
 294   else
 295   {
 296     log_message(MY_WARNING_LEVEL,
 297                 ER_DEFAULT(ER_WARN_DEPRECATED_SYNTAX_NO_REPLACEMENT),
 298                 name);
 299   }
 300 }
```

How to repeat:
See the code

Suggested fix:
Change the function option_deprecation_warning() to:

```
 285 static void option_deprecation_warning(MYSQL_THD thd, const char* name)
 286 {
 287   if (thd != NULL)
 288   {
 289     push_warning_printf(thd, Sql_condition::SL_WARNING,
 290                         ER_WARN_DEPRECATED_SYNTAX_NO_REPLACEMENT,
 291                         ER_THD(thd, ER_WARN_DEPRECATED_SYNTAX_NO_REPLACEMENT),
 292                         name);
 293   }
 294   log_message(MY_WARNING_LEVEL,
 295               ER_DEFAULT(ER_WARN_DEPRECATED_SYNTAX_NO_REPLACEMENT),
 296               name);
 297 }
```

Posted by developer:
 
Thank you for your feedback, this has been fixed in upcoming versions and the following was added to the 5.7.26 / 8.0.15 changelog:
Whenever you use group_replication_allow_local_disjoint_gtids_join, which is deprecated, a log message is added.

Posted by developer:
 
Correction: this was added to the 5.7.26 change log only, the variable was removed from 8.0 already