Add ability to download/upload connector configs

RedPanda is a very nice and feature-rich UI and has really helped our team improve our Kafka operations.

One of the few features that my team still greatly admires from Confluent's Control Center (C3) is the ability to download connector configs (as JSON or properties files) and then similarly upload connector configurations.

This is typically used for various purposes, such as backup and restore when a connector needs to be rebooted or during deployment to multiple environments with minor tweaks between the connector definitions. Consider how tedious and error-prone it would be to delete and relaunch a connector through the UI one configuration at a time.

Would be nice if this feature saw its way into RedPanda console also.

Thank you for providing this tool to the community and for all the hard work you've put into making this tool great.

No files, tests, or entry points are named. Start by tracing the existing connector management flow and its API boundary, then define how configuration downloads should represent JSON and properties files and how uploads should validate them. Done means users can export a connector configuration and import it for backup, restore, or deployment with edits.