UnsealRequest is missing the migrate option

[dtrts]

Describe the feature request or question

This client library is unable to proivde an unseal key with the migrate option set to true.

Current schema.UnsealRequest:
https://github.com/hashicorp/vault-client-go/blob/main/schema/model_unseal_request.go

Current API endpoint definition:
https://developer.hashicorp.com/vault/api-docs/system/unseal

The post body includes the migrate option for seal migration. I would like this to be included to perform seal migrations using this client library.

Link to the Vault API Docs that support this feature

https://developer.hashicorp.com/vault/api-docs/system/unseal