Improve handling of Vault errors

[dadgar]

This PR does the following:

1. Adds recoverable error handling to the Client when it fails to Unwrap a token.
2. Adds better response validation that displays Warnings returned from Vault.
3. Vendors in Don't swallow logical.Unwrap error vault#4258 which fixes an issue
   where Vault's api would swallow an error that could have resulted from the
   underlying network.

Fixes #4097

[github-actions]

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