Add "am capabilities" for tools probling

There is no way to know which command/flags are supported in am.
This CL adds a "capability" command which allows to probe
programatically.

Test: NA
Bug: 265460189
Change-Id: If50269251a6907968e7c8afe10bf873f25338b91
diff --git a/proto/src/OWNERS b/proto/src/OWNERS
index ccff624..4d898b41 100644
--- a/proto/src/OWNERS
+++ b/proto/src/OWNERS
@@ -3,3 +3,4 @@
 per-file camera.proto = file:/services/core/java/com/android/server/camera/OWNERS
 per-file system_messages.proto = file:/core/res/OWNERS
 per-file altitude.proto = file:/location/OWNERS
+per-file am_capabilities.proto = rpaquay@google.com, sanglardf@google.com
diff --git a/proto/src/am_capabilities.proto b/proto/src/am_capabilities.proto
new file mode 100644
index 0000000..d97bf81
--- /dev/null
+++ b/proto/src/am_capabilities.proto
@@ -0,0 +1,12 @@
+syntax = "proto3";
+
+package com.android.server.am;
+option java_multiple_files = true;
+
+message Capability {
+  string name = 1;
+}
+
+message Capabilities {
+  repeated Capability values = 1;
+}