Add `Memo` option to Send dialog

Dash has the ability to add a `memo` to a transaction, as we've demonstrated in https://github.com/dashhive/examples/tree/master/apps/next-app-router and at https://dash-incubator-next-app-router-memo.vercel.app/.

We should add an optional memo field to the Send Dialog, this will allow manually interacting with Maya and ease our built-in implementation as well.