Add messages for CRUDL operations

[cedric-cordenier]

Requires

Supports

[github-actions]

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[prashantkumar1982]

Optional: proto allows us to tag some fields as optional, to indicate they can be omitted, and easily checked in code with logic.

Example :
message SecretResponse {
.
.
optional string encrypted_value = 2;
optional string error = 4;
}

Then in go code:
secretResponse.has_error() OR
secretResponse.has_encryptedValue()

This is instead of directly checking if these are empty strings.

[DeividasK]

My preference would be to split this into

message SecretResponse {
  SecretIdentifier id = 1;

  oneof result {
    SecretData success_data = 2;
    string error = 3;
  }
}

message SecretData {
  string encrypted_value = 1;
  repeated EncryptedShares encrypted_decryption_key_shares = 2;
}

[cedric-cordenier]

I went with the oneof :)