Migrate Etherscan calls to new proxy

[nvonpentz]

We have new proxies deployed, so we should update the codebase to point to the new URLs. The response schema has changed slightly (no more wrapper with lastUpdated), so well need to update ParseTokenInfo incomponents/brave_wallet/browser/asset_ratio_response_parser.cc to parse the new response format.

Also we'll need to add the Brave Services Key if it's not included already.

[kjozwiak]

@srirambv going to label this one as QA/Yes so we can quickly verify that the Stripe onramp is working as mentioned via brave/brave-core#19566 (comment). The above requires 1.57.41 or higher for 1.57.x verification 👍

[srirambv]

Verified as part of #31397 (comment). Just ensured that Stripe option is shown only for US and when selecting a particular token and selecting Stripe loads the selected token and the input amount.