The network doesn't increase the gas price when the demand rises

[xgreenx]

The static gas price leads to the problem that attackers can spam the network with cheap transactions that consume the whole block. Thanks to https://github.com/FuelLabs/fuel-core/issues/1909 and the tips system, people can still raise the price by themself via the transaction pool. But still, the network should secure itself instead of relying on users.

Dynamic gas prices feature https://github.com/FuelLabs/fuel-core/issues/1624 should fix this problem.