Update token metadata

Signed-off-by: Nikolai Rodionov <allanger@badhouseplants.net>

proto/tokens/v1/tokens_v1.proto

@@ -29,9 +29,13 @@ message TokenMetadata {
   string name = 1;
   // Token expiration timestamp
   google.protobuf.Timestamp expires_at = 2;
+  // When the token was used the last time
   google.protobuf.Timestamp last_used_at = 3;
+  // When was the current token generated
   google.protobuf.Timestamp generated_at = 4;
+  // When was the current token entry created
   google.protobuf.Timestamp created_at = 5;
+  // When was the token revoked
   google.protobuf.Timestamp revoked_at = 6;
 }