Change the default values of the Spider plugin variables from -1 (use table value) to the default table values. Also, deprecate the option value -1 (use table value).

For example, the current default plugin value of spider_auto_increment_mode is -1 (use table value) and the current default table value is 0 (normal mode). Thus, the real default value is 0. I do like to remove this indirection (just set the default server value to 0).

The default table values are defined in spider_set_connect_info_default().

The following documents should be updated at least (MDEV-26365):

• https://mariadb.com/kb/en/spider-server-system-variables/

Here is the list of the plugin variables whose default values should be updated: