* Replace external KMS backend logic for AWS, Azure, and GCP with go-kms-wrapping
* Move kms client setup config into its own package for easier parsing
* Update kms integration flag naming
* Error if nil storage is passed to external KMS
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Signed-off-by: Daniel Weiße <dw@edgeless.systems>
So far the masterSecret was sent to the initial bootstrapper
on init/recovery. With this commit this information is encoded
in the kmsURI that is sent during init.
For recover, the communication with the recoveryserver is
changed. Before a streaming gRPC call was used to
exchanges UUID for measurementSecret and state disk key.
Now a standard gRPC is made that includes the same kmsURI &
storageURI that are sent during init.
In the light of extending our eKMS support it will be helpful
to have a tighter use of the word "KMS".
KMS should refer to the actual component that manages keys.
The keyservice, also called KMS in the constellation code,
does not manage keys itself. It talks to a KMS backend,
which in turn does the actual key management.
