Add is_exported field to aconfig.proto

When a flag is exported, it can be read by code built in other containers. By
default flags are not exported. Set this to true if your flag is gating
a public API which may be called from other containers (typically, a
flag used in @FlaggedAPI annotations).

Test: atest aconfig.test
Bug: 311152500
Change-Id: I53e3ed18b96c1518f04172d5933ef96b41ccda7e
diff --git a/tools/aconfig/protos/aconfig.proto b/tools/aconfig/protos/aconfig.proto
index d5e2868..9e193ec 100644
--- a/tools/aconfig/protos/aconfig.proto
+++ b/tools/aconfig/protos/aconfig.proto
@@ -40,6 +40,7 @@
   optional string description = 3;
   repeated string bug = 4;
   optional bool is_fixed_read_only = 5;
+  optional bool is_exported = 6;
 };
 
 message flag_declarations {
@@ -77,6 +78,8 @@
   optional flag_permission permission = 7;
   repeated tracepoint trace = 8;
   optional bool is_fixed_read_only = 9;
+  optional bool is_exported = 10;
+
 }
 
 message parsed_flags {