Update the GraphQL schema for updateAsset to include setFee

[JoblersTune]

Prior to feat: liquidity webhooks #1782 there was an updateWithdrawlThreshold mutation for assets. But since liquidity updates were added as well now there's an updateAsset mutation. Since there is a general updateAsset mutation it would make sense to move the setFee mutation into the updateAsset mutation as well.

Edit: the createAsset mutation should also have an option to add fees immediately then as well.