Add wait API endpoint for waiting on process exit

Signed-off-by: Michael Crosby <crosbymichael@gmail.com>

api/next.pb.txt

@@ -3576,6 +3576,45 @@ file {
       json_name: "metrics"
     }
   }
+  message_type {
+    name: "WaitRequest"
+    field {
+      name: "container_id"
+      number: 1
+      label: LABEL_OPTIONAL
+      type: TYPE_STRING
+      json_name: "containerId"
+    }
+    field {
+      name: "exec_id"
+      number: 2
+      label: LABEL_OPTIONAL
+      type: TYPE_STRING
+      json_name: "execId"
+    }
+  }
+  message_type {
+    name: "WaitResponse"
+    field {
+      name: "exit_status"
+      number: 1
+      label: LABEL_OPTIONAL
+      type: TYPE_UINT32
+      json_name: "exitStatus"
+    }
+    field {
+      name: "exited_at"
+      number: 2
+      label: LABEL_OPTIONAL
+      type: TYPE_MESSAGE
+      type_name: ".google.protobuf.Timestamp"
+      options {
+        65010: 1
+        65001: 0
+      }
+      json_name: "exitedAt"
+    }
+  }
   service {
     name: "Tasks"
     method {
@@ -3658,6 +3697,11 @@ file {
       input_type: ".containerd.services.tasks.v1.MetricsRequest"
       output_type: ".containerd.services.tasks.v1.MetricsResponse"
     }
+    method {
+      name: "Wait"
+      input_type: ".containerd.services.tasks.v1.WaitRequest"
+      output_type: ".containerd.services.tasks.v1.WaitResponse"
+    }
   }
   options {
     go_package: "github.com/containerd/containerd/api/services/tasks/v1;tasks"