Proto commits in containerd/ttrpc

These 8 commits are when the Protocol Buffers files have changed:

Commit:336fc1b
Author:Maksym Pavlenko

Add integration test to reproduce issue with empty payloads Signed-off-by: Maksym Pavlenko <pavlenko.maksym@gmail.com>

The documentation is generated from this commit.

Commit:86d3c77
Author:Derek McGowan
Committer:Derek McGowan

Add stream tests Signed-off-by: Derek McGowan <derek@mcg.dev>

Commit:84187a8
Author:Derek McGowan
Committer:Derek McGowan

Add integration test package Signed-off-by: Derek McGowan <derek@mcg.dev>

Commit:d240c50
Author:Kazuyoshi Kato
Committer:Kazuyoshi Kato

Use google.golang.org/protobuf instead of github.com/gogo/protobuf This change replaces github.com/gogo/protobuf with google.golang.org/protobuf, except for the code generators. All proto-encoded structs are now generated from .proto files, which include ttrpc.Request and ttrpc.Response. Signed-off-by: Kazuyoshi Kato <katokazu@amazon.com>

Commit:4b957e7
Author:Michael Crosby

Update imports and references for containerd This updates the references and imports for the move into the containerd org. Signed-off-by: Michael Crosby <crosbymichael@gmail.com>

Commit:809ed49
Author:Stephen J Day

ttrpc: remove unused imports Signed-off-by: Stephen J Day <stephen.day@docker.com>

Commit:bd8c759
Author:Stephen J Day

ttrpc: update examples after name change Signed-off-by: Stephen J Day <stephen.day@docker.com>

Commit:eb6cfbb
Author:Stephen J Day

mgrpc: baseline protobuf example Set the stage for the example server by including a service definition, generated code and the protobuild definition file used to generate them. From here, we can work up to a generated mgrpc server. Signed-off-by: Stephen J Day <stephen.day@docker.com>