Support dapps suggesting chains to be added to the user's wallet application

### Overview

Inspired by EIP-3085, this design allows Solana applications ("dapps") to suggest chains to be added to the user's wallet application. The wallet application may arbitrarily refuse or accept the request. We have received a request for this feature from many dapps.

### Desired Outcome

The desired outcome is for dapps that are on testnets, canary chains, or other SVM chains to be able to conveniently prompt their users to switch networks and seamlessly interact with their dapp and see their assets rather than requiring complex manual custom RPC changes. As more SVM chains spin up, this can prevent a mess with multiple standards and one-off implementations down the line.

### Implementation

1. Solana Wallet Standard: At first glance there are some changes needed to the Solana wallet standard. There are places where the wallet is required to return all chains that it supports, so we would need some interface for the dapp to pass back a new chain to be added: https://github.com/solana-labs/wallet-standard/blob/master/packages/wallets/solflare/src/account.ts#L25 This change seems like it could be made immediately if it is done in a non-breaking way. The wallet should not be required to add a chain even if the dapp requests it.
2. Wallet Adapter: We would need to make some change to the wallet adapter so the dapp can specify the desired RPC network. This would need to be rolled out after the Wallet Standard change.
3. Dapp Support: The dapp updates their Wallet Adapter library and specify their desired RPC network. If no RPC network is specified, by default this change has no effect - the behavior is exactly the same as SVM wallets function right now (default to Solana mainnet). This is the last change to occur.