refactor(rainbowkit-wallets): multiple providers with link

[elboletaire]

depends on vocdoni/saas-backend#315

This pull request introduces support for linking SaaS OAuth accounts without persisting authentication tokens or wallet data, and adds comprehensive tests for the new and existing OAuth flows. It refactors the wallet creation process to allow control over persistence and updates the OAuth connector to support both login and account linking modes. The most important changes are grouped below:

SaaS OAuth Linking Functionality

• Added a new linkSaasOAuth utility that allows linking a SaaS OAuth account without persisting authentication tokens or wallet data, and ensures the proper API endpoint and headers are used. (linkSaasOAuth.ts, index.ts) [1] [2]
• Added tests for the new linking functionality to ensure correct behavior and no persistence of sensitive data. (linkSaasOAuth.test.ts)

OAuth Connector Enhancements

• Updated saasOauthConnector to support both 'login' and 'link' modes, with dynamic endpoint selection and conditional token persistence. Added options for mode and token retrieval. (saasOauthConnector.ts) [1] [2] [3]
• Added comprehensive tests for the connector to verify correct token storage on login and no storage on linking, as well as correct API usage. (saasOauthConnector.test.ts)

Wallet Persistence Control

• Modified localStorageWallet.createWalletFromData and dependent flows to accept a persist option, allowing wallet creation without saving to local storage (used in linking scenarios). (localStorageWallet.ts, saasOauthWallet.tsx, localStorageWallet.test.ts) [1] [2] [3] [4]