Allow translation of input placeholder

Allow translation of input placeholder - patch.

Added a schema.yml so the fields can be translated using the default block translation interface.

In the meantime you can just apply https://git.drupalcode.org/project/search_api_block/-/merge_requests/10.... until things get merged :-)

Thank you! The schema has been merged.

Automatically closed - issue fixed for 2 weeks with no activity.