Creates a template for the next block.
- blocktemplate_blob — string; hex-encoded serialized block template.
- difficulty — unsigned int, difficulty for the block template.
- height — unsigned int, height corresponding to the block template.
- wallet_address - address where transferred block reward
- stakeholder_address - used only in PoS mining, address where returned stake which was used in PoS generation (optional, normally is the same as wallet_address)