Use JSON data type for dataset column in dataset table

[brotkrueml]

As TYPO3 v12 will raise the database requirements and supports the JSON data type, the type of the dataset column in the tx_jobrouterdata_domain_model_dataset should be moved from TEXT to JSON. This makes it possible to select rows directly within a SELECT statement instead of filtering via PHP.

• Use JSON as data type for dataset column.
• Adjust documentation.
• Add breaking entry to changelog.

As the dataset column should contain always valid JSON this should produce no errors on migration.