Because Ztunnel can have Istio semantics baked in, we do not need to encode all this information on the wire.
Instead, an Istio specific field like `ExpectedTLSIdentity: spiffe://foo.bar` can encode the same information, at a fraction of the cost.

In our testing, even the most generous representations give custom types a 10x edge (in size, allocations, and CPU time) over Envoy types.

  // `limitResponse` indicates what to do with requests that can not be executed right now
  optional LimitResponse limitResponse = 2;

  // `lendablePercent` prescribes the fraction of the level's NominalCL that
  // can be borrowed by other priority levels. The value of this
  // field must be between 0 and 100, inclusive, and it defaults to 0.

  // `limitResponse` indicates what to do with requests that can not be executed right now
  optional LimitResponse limitResponse = 2;

  // `lendablePercent` prescribes the fraction of the level's NominalCL that
  // can be borrowed by other priority levels. The value of this
  // field must be between 0 and 100, inclusive, and it defaults to 0.

  // `limitResponse` indicates what to do with requests that can not be executed right now
  optional LimitResponse limitResponse = 2;

  // `lendablePercent` prescribes the fraction of the level's NominalCL that
  // can be borrowed by other priority levels. The value of this
  // field must be between 0 and 100, inclusive, and it defaults to 0.

  // `limitResponse` indicates what to do with requests that can not be executed right now
  optional LimitResponse limitResponse = 2;

  // `lendablePercent` prescribes the fraction of the level's NominalCL that
  // can be borrowed by other priority levels. The value of this
  // field must be between 0 and 100, inclusive, and it defaults to 0.