Make Max Number of Posts Filterable

[kevinfodness]

Description

The maximum number of posts is hardcoded to 10, but should be filterable. It's used in Gutenberg here to set the upper bound of the range control: https://github.com/alleyinteractive/wp-curate/blob/develop/blocks/query/edit.tsx#L293

Use Case

As a developer, I want to be able to modify the max number of posts that is available in the range control in a Query block.

Acceptance Criteria

• Add a filter in PHP to set the max number of posts for the query block. Default it to 10.
• Use wp_localize_script to make this value available to the editor script for the block.
• If this value is set, have the edit component for the block use it instead of the default that comes in from attributes.