Add key_type, under seal for Azure KeyVault.

[joachimsmits]

Feature:
We would like to see the option "key_type", under seal for Azure KeyVault.

Reason:
A policy is block for us, because key type should be RSA_HSM and not default RSA.

Example:
seal "azurekeyvault" {
tenant_id = "46646709-b63e-4747-be42-516edeaf1e14"
client_id = "03dc33fc-16d9-4b77-8152-3ec568f8af6e"
client_secret = "DUJDS3..."
vault_name = "hc-vault"
key_name = "vault_key"
key_type = "RSA-HSM"
}