Plaid Create Link Token

The `/link/token/create` endpoint creates a `link_token`, which is required as a parameter when initializing Link. Once Link has been initialized, it returns a `public_token`, which can then be exchanged for an `access_token` via `/item/public_token/exchange` as part of the main Link flow. A `link_token` generated by `/link/token/create` is also used to initialize other Link flows, such as the update mode flow for tokens with expired credentials, or the Payment Initiation (Europe) flow.