Ensure gasFeeCap and priorityFeeCap are fetched at the same height

[lumtis]

Describe the Issue
From the current logic gasFeeCap and priorityFeeCap at a different height and breaking the invariant gasFeeCap>=priorityFeeCap

This required the fix #2950

The values are fetched in two different query in

node/zetaclient/chains/evm/observer/observer_gas.go

Line 54 in b56e758

func (ob *Observer) PostGasPrice(ctx context.Context) error {

Possible solution
Fetch first the current height of the chain, then perform both query for this specific height.