Fund Ephemeral Account RPC
Introduce a new RPC call which allows funding an ephemeral account. These accounts are introduced in #3695, in short they are off-chain balances kept on the host and can be used as payment method. Currently there is no way to put money on those accounts. Add an RPC that allows this. Payment is made directly from a contract the caller has with the host.
The ephemeral accounts will serve as a payment method to pay for RPCs. The benefit of using such an account is that it does not require any disk I/O nor interaction with the blockchain. Amongst a lot of other things this allows speedy downloads. We need this for CDN and file sharing use cases.