"Support translation of search bar"

[Kxka]

What does this Pull Request do?

Provide a brief description of what the intended result of the PR will be and/or what
problem it solves.

• Related GitHub Issue: [FEATURE] Search Block to support translation #74

What's new?

Added a schema definition for search block that marks these fields as translatable.

How should this be tested?

Install and enable your desired languages in Admin > Config > Regional and Language > Languages
Enable the content translation module
Enable the configuration translation module

If the page is not in default language e.x. https://islandora.dev/fr/collections, translate block option should show

Clicking in should give configuration to change the placeholder and button text

Documentation Status

• Does this change existing behaviour that's currently documented?
• Does this change require new pages or sections of documentation?
• Who does this need to be documented for?
• Associated documentation pull request(s): ___ or documentation issue ___

Additional Notes:

Any additional information that you think would be helpful when reviewing this
PR.

Interested parties

Tag (@ mention) interested parties or, if unsure, @Islandora/committers