Reduce MetaMask Default Suggested Gas

• Right now, gas fee suggestions are way higher than they need to be for an OnChain boost (MetaMask default is 40 GWEI, ~$1.30+)
• When users OnChain boost, we can set the default suggestion in MetaMask to something lower and more reasonable.

Here is an approach that @benhayward.ben discovered: https://github.com/MetaMask/metamask-extension/issues/1473

We can decide what threshold we want the default to be at. I have safely cut the fee by around 70% and it still settled in under a minute. We can cut it by ~40-50% of the default suggestion to be safe. This should run in parallel with our onchain updates.

@jotto141 @ottman @markeharding