aconfig: add storage file type into storage file serialization

1, add storage file type into storage files serialization
2, update aconfig_storage_read_api integration tests to not rely on
soong to produce read only storage files. Instead, have the test process
create temp read only storage file copies.

Bug: b/312444587
Test: atest aconfig.test; atest.aconfig_storage_file.test
Change-Id: I1607fb000b48e8acffc966b16a5136578911ab3e

tools/aconfig/aconfig_storage_write_api/src/flag_value_update.rs

@@ -51,15 +51,16 @@ pub fn update_boolean_flag_value(
 #[cfg(test)]
 mod tests {
     use super::*;
-    use aconfig_storage_file::FlagValueList;
+    use aconfig_storage_file::{FlagValueList, StorageFileType};
 
     pub fn create_test_flag_value_list() -> FlagValueList {
         let header = FlagValueHeader {
             version: FILE_VERSION,
             container: String::from("system"),
-            file_size: 34,
+            file_type: StorageFileType::FlagVal as u8,
+            file_size: 35,
             num_flags: 8,
-            boolean_value_offset: 26,
+            boolean_value_offset: 27,
         };
         let booleans: Vec<bool> = vec![false; 8];
         FlagValueList { header, booleans }