[FEATURE REQ] [Key Vault] Add configuration flag to delegate all cryptographic operations to service

[vcolin7]

Is your feature request related to a problem? Please describe.
From @sfc-gh-bschmidt:

[The CryptographyClient] doesn't allow us to configure [it] to not even try retrieving the local key. Using a version without support for completely disabling the local key retrieval would cause the following regressions for us:

• We're using the key vault library to access a large number of customer managed keys. The cryptography clients are very short-lived. Trying the retrieval of the local key even once per client instance will introduce significant additional overhead and latency.

• For each client creation with a customer managed key, customers will suddenly start seeing a denied Get operation in their access logs.

Describe the solution you'd like

[...] add support for configuring CryptographyClientBuilder to disable the local client completely

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