Wallet should attempt to reconnect to the node after the conenction was lost.

Currently, when the node is restarted, the wallet has to be restarted as well.

Also note that since https://github.com/mintlayer/mintlayer-core/pull/2063 `Wallet` holds a `MempoolConfig` obtained from the node. So after the reconnection is made, the stored `MempoolConfig` will have to be updated, because the node configuration could have been changed.