This normalizes the SecretData serialization from the client to address #981.
When serializing objects sent to the service with secrets, we would turn it into a SecretData
We use SecretData to convert this:
`{"auth": {"user": "A", "personal_access_token": "B"}}`
to this:
`"auth": { "secret": { "url": "https://KEYVAULT-URL" }}`
Currently, in the case we have a SecretData we've not yet saved, the serialized form looks like this:
`{"auth": { "secret": {"user": "A", "personal_access_token": "B"}}}`
This PR simplifies the client side serialization to this:
`{"auth": {"user": "A", "personal_access_token": "B"}}`
