Add CLI Command for Bulk Sync

[kevinfodness]

Description

By default, the page size is 100, which is fine for cron, but will take a long time to execute for a large number of videos if run hourly (the default). We should have a CLI option to sync all videos with a larger batch size (can be set per adapter, JW Player is 10,000, for example).

Use Case

When setting up this functionality initially, it would be good to have a method for importing videos in bulk.

Acceptance Criteria

• When a new instance of Sync_Manager is initialized, also register a CLI command for bulk indexing videos using the provided adapter and callback.
• Allow the bulk size parameter to be overridden via a CLI argument, similar to how we have done it for SearchPress. By default, it will use the same bulk size that was provided when the sync manager was initialized, but CLI users can override it with a different value, e.g., wp video-sync sync --batch_size=10000