bugfix/handle empty response

[Sledro]

• Prevent panic in case where RPC returns an empty body: panic: interface conversion: interface {} is nil, not map[string]interface {}
• Add new CLI commands to readme

[CryptoKass]

This looks good to me. There is only one very mild issue, so it is still safe to merge as is, but:

RE: cli/cmd/defender_defendda.go
Its possible for DefendDA to fail for many reason, but we are always logging: please wait for Celestia validators to commit data root in the error.

Ideally the message should only be shown when the error contains: "no data commitment has been generated for the provided height"

tx, err := d.DefendDA(blockHash)
 		if err != nil {
 			logger.Error("Failed to defend data availability, please wait for Celestia validators to commit data root", "err", err)