Add migration for available_for_sequencing field and update sample handling

Commit notes

- Implemented a new migration function to add the available_for_sequencing column to the samples table, ensuring existing samples are updated with a default value of true. - Enhanced sample retrieval in the MarketHandler and SamplePackHandler to conditionally load samples based on their availability for sequencing. - Updated the Sample model to include the available_for_sequencing field and adjusted related request and response models accordingly. - Introduced UI elements in SampleTreeView to display and toggle the available_for_sequencing status for samples, improving user interaction and management capabilities.