Automatic merge from submit-queue
Add Google cloud KMS service for envelope encryption transformer
This adds the required pieces which will allow addition of KMS based encryption providers (envelope transformer).
For now, we will be implementing it using Google Cloud KMS, but the code should make it easy to add support for any other such provider which can expose Decrypt and Encrypt calls.
Writing tests for Google Cloud KMS Service may cause a significant overhead to the testing framework. It has been tested locally and on GKE though.
Upcoming after this PR:
* Complete implementation of the envelope transformer, which uses LRU cache to maintain decrypted DEKs in memory.
* Track key version to assist in data re-encryption after a KEK rotation.
Development branch containing the changes described above: https://github.com/sakshamsharma/kubernetes/pull/4
Envelope transformer used by this PR was merged in #49350
Concerns #48522
Planned configuration:
```
kind: EncryptionConfig
apiVersion: v1
resources:
- resources:
- secrets
providers:
- kms:
cachesize: 100
configfile: gcp-cloudkms.conf
name: gcp-cloudkms
- identity: {}
```
gcp-cloudkms.conf:
```
[GoogleCloudKMS]
kms-location: global
kms-keyring: google-container-engine
kms-cryptokey: example-key
```
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