Add support for encoding error structure for grpc errors

[jsternberg]

This adds support for encoding the error structure for grpc errors. It
does this by using the details to encode any wrapped errors.

Each error is composed of a Status protobuf. The message included in
that status is the default error message if no additional details are
provided. The first detail is an encoding of the error if one was given.
If there was no encoding possible or it wasn't possible to deserialize
it, a generic error is created with the original message.

Any additional details are any wrapped errors. Each wrapped error is a
Status that follows the same encoding scheme. This allows an error to
wrap multiple errors and the implementation isn't dependent on the
contents.

[jsternberg]

This is an alternative to #7. I think this implementation might be better because it doesn't rely on the contents of the messages and the structure is encoded directly into the serialization scheme.

Still needs some tests and I'd like to add some functionality to enable the currently existing serialization that buildkit uses for some backwards compatibility, but I wanted to get this idea out there first before spending time on that.

[jsternberg]

A more complete and bug free implementation of this is created here: moby/buildkit#5203

I figured it was probably easier to update the buildkit serialization format there and then move that code here when it was ready than it was to write the code here and transition buildkit. That way, we'll at least know it works before it is merged and starts to be used here.

[dmcgowan]

I'm going to close this one since the other is merged and heavily conflicts. Feel free to open one based on what you learned with the serialization in the buildkit PR. We should be able to rely on the new unit tests to either check for the same behavior or at least detect how it might be different.