feat(unseal): add unseal protocol support for user agents

protobufs/unseal.proto

@@ -2,13 +2,20 @@ syntax = "proto3";
 
 package arbiter.unseal;
 
-message UserAgentKeyRequest {}
+import "google/protobuf/empty.proto";
 
-message ServerKeyResponse {
+message UnsealStart {}
+
+message UnsealStartResponse {
   bytes pubkey = 1;
 }
-message UserAgentSealedKey {
-  bytes sealed_key = 1;
-  bytes pubkey = 2;
-  bytes nonce = 3;
+message UnsealEncryptedKey {
+  bytes key = 1;
+}
+
+enum UnsealResult {
+  UNSEAL_RESULT_UNSPECIFIED = 0;
+  UNSEAL_RESULT_SUCCESS = 1;
+  UNSEAL_RESULT_INVALID_KEY = 2;
+  UNSEAL_RESULT_UNBOOTSTRAPPED = 3;
 }