Support backup API URLs

Summary: Support backup API URLs

Test Plan:
Edit the REACT_APP_BCHA_APIS variable in .env to purposefully include error-generating APIs:

REACT_APP_BCHA_APIS=fakenews,stillnotreal,https://free-test.fullstack.cash/v3/,https://rest.kingbch.com/v3/,https://wallet-service-prod.bitframe.org/v3/,notevenaurl

Install dependencies and run the app locally in your browser:

npm install --legacy-peer-deps
npm start

Observe that the app loads in an error state. It then proceeds to cycle through the API URLs in REACT_APP_BCHA_APIS until the wallet is loaded successfully.

Reviewers: alcipir, #bitcoin_abc, deadalnix

Reviewed By: #bitcoin_abc, deadalnix

Differential Revision: https://reviews.bitcoinabc.org/D8575