docs: add signer response to submit-data page

> - Account opacity: You will not know which subaccount signed which blob. Subaccounts are managed automatically by the node.

from [comment](https://github.com/celestiaorg/docs/pull/2281/files#r2471925053)


- core PR https://github.com/celestiaorg/celestia-core/pull/2593
- adding the types to the response to the sdk https://github.com/celestiaorg/cosmos-sdk/pull/694