add option for request template

right now it's hardcoded to `await window.ethereum.request({...jsonrpcRequest})` but it should be configurable.

Ideally it should default to using something like `window.fetch({method: "POST", body: JSON.stringify({...jsonrpcRequest})` and the MetaMask one configures it to be `window.ethereum.request`

No file, test, or entry point is named in the issue. Start by locating the hardcoded window.ethereum.request call in the Docusaurus OpenRPC interactive documentation, then trace how MetaMask-specific behavior is configured. Done means requests use a configurable template, default to the described window.fetch form, and retain MetaMask's window.ethereum.request behavior.

Written by the indexing model from the issue text.