api, linux/runcopts: ensure output is current

Ensure that the descriptors are re-generated on the CI and block merges
that don't include updates. We also enable the `check-protos` check as
part of this process. The installation process for protobufs has been
fixed to support protobuild.

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

linux/runcopts/next.pb.txt

@@ -5,17 +5,31 @@ file {
   message_type {
     name: "RuncOptions"
     field {
-      name: "criu_path"
+      name: "runtime"
       number: 1
       label: LABEL_OPTIONAL
       type: TYPE_STRING
+      json_name: "runtime"
+    }
+    field {
+      name: "runtime_root"
+      number: 2
+      label: LABEL_OPTIONAL
+      type: TYPE_STRING
+      json_name: "runtimeRoot"
+    }
+    field {
+      name: "criu_path"
+      number: 3
+      label: LABEL_OPTIONAL
+      type: TYPE_STRING
       json_name: "criuPath"
     }
     field {
       name: "systemd_cgroup"
-      number: 2
+      number: 4
       label: LABEL_OPTIONAL
-      type: TYPE_STRING
+      type: TYPE_BOOL
       json_name: "systemdCgroup"
     }
   }