Fee model: take into account blob computation overhead when calculating pubdata_price

[perekopskiy]

For each blob created there is some calculation done that eventually has to be proven and the number of cycles is not negligible (in terms of cycles, one blob = tens of average txs).
We need to adjust pubdata price to take it into account. Formula: pubdata_price += native_price * NATIVE_PER_BLOB

[EmilLuta]

There's a doc and some estimation work by @perekopskiy. Can't find the doc, but will be added by Misha later. This is not yet finalized (IMO).