Remove requisite for a signature on page refreshes

[elisealix22]

Currently every time the app reloads, a new signature is required. It's a top developer ask to persist the signature between refreshes. This issue's purpose is to track the popular request, however we likely won't have a fix until we have a more secure key management system.

Note: We are also now tracking this in our FAQ https://github.com/xmtp/docs/blob/main/docs/faq.md#why-does-my-app-request-a-new-signature-for-xmtp-when-i-refresh-my-browser