Added exported keychain settings to provide mirrornet configuration to the wallet

examples/ts/signature-extension/__tests__/assets/settings.kc

+{"current_rpc":{"chainId":"4200000000000000000000000000000000000000000000000000000000000000","testnet":true,"uri":"https://api.fake.openhive.network"},"rpc":[{"chainId":"4200000000000000000000000000000000000000000000000000000000000000","testnet":true,"uri":"https://api.fake.openhive.network"}],"switchRpcAuto":false}
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