Return more verbose error messages on settlement init

[omritoptix]

Currently if not rollapp/sequencer found on init, "key not found" is return. The error should be prefixed by which object exactly was not found by prefixing the err with the reason.

if err != nil {
		if err == ErrBatchNotFound {
			endHeight = 0
		} else {
			return err
		}
	} else {
		endHeight = latestBatch.EndHeight
	}
	b.latestHeight = endHeight
	b.logger.Info("Updated latest height from settlement layer", "latestHeight", endHeight)
	b.sequencersList, err = b.fetchSequencersList()
	if err != nil {
		return err
	}

[mtsitrin]

closed by #379