Graceful error handling

[riptl]

The plugin currently has two error handling modes: panic_on_db_errors or "log error and ignore".

Occasional errors sending data to PostgreSQL are expected however, e.g. when the DB host reboots or if there is a network blip.
Therefore in production "log error and ignore" is the only choice.

Since Solana mainnet does several thousand updates per second to accounts this results in a flood of error messages in the log in the case of downtime.

To reduce the error rate, I suggest the workers should back off exponentially with writes until Postgres is back up by introducing sleeps.