Implement syncing from genesis without downloading data blobs

[musalbas]

We should implement the ability for celestia-core nodes to sync the chain from genesis by only downloading the sdk.Txes (so that they can recompute the state root) but not the actual blob data (they should assume that the data root is valid).

In line with the expectation that the Celestia network is not expected to store historical blob data forever, this would then allow for celestia-core archive nodes to prune historical blob data, without destroying the ability for full nodes to sync the celestia-app state from genesis.

In other words, implement partial storage nodes that only download and check the data in the reserved namespace.

[musalbas]

related: #931

[musalbas]

related celestia-node issue: celestiaorg/celestia-node#2033

[musalbas]

related discoverability issue: #995