Pass apex_info.pb file to delta_generator

target_files contain META/apex_info.pb, which contains metadata about
compressed apexes. Extract this file from target_file.zip, and pass it
to delta_generator. delta_generator will then copy these data to
update_metadata

Test: generate an OTA
Bug: 172911822
Change-Id: Ia4babb9e711a92f2b78ef8e1dd6ad35d0a2bb5a8
diff --git a/update_metadata.proto b/update_metadata.proto
index 5e86f8f..a1f093c 100644
--- a/update_metadata.proto
+++ b/update_metadata.proto
@@ -359,10 +359,16 @@
 // Definition has been duplicated from
 // $ANDROID_BUILD_TOP/build/tools/releasetools/ota_metadata.proto. Keep in sync.
 message ApexInfo {
-  required string package_name = 1;
-  required int64 version = 2;
-  required bool is_compressed = 3;
-  required int64 decompressed_size = 4;
+  optional string package_name = 1;
+  optional int64 version = 2;
+  optional bool is_compressed = 3;
+  optional int64 decompressed_size = 4;
+}
+
+// Definition has been duplicated from
+// $ANDROID_BUILD_TOP/build/tools/releasetools/ota_metadata.proto. Keep in sync.
+message ApexMetadata {
+  repeated ApexInfo apex_info = 1;
 }
 
 message DeltaArchiveManifest {