Issue #1496510: Convert search settings to configuration system.

PR for https://github.com/backdrop/backdrop-issues/issues/170
I don't think we have a group for "config_upgrade", so this line of docblock should be removed.

Additionally, we usually add a group before and after all 1xxx updates. Since this is the first update to Search module, we'll need to add these groups:

Before this function add:
```
/**
 * @addtogroup updates-7.x-to-1.x
 * @{
 */
```

And afterwards at the bottom of the file:
```
/**
 * @} End of "addtogroup updates-7.x-to-1.x"
 * The next series of updates should start at 2000.
 */
 ```

See contact module's contact.install for an example.