Add feature flag for disallow_cellular_null_ciphers

Adds a new aconfig file in android.os and creates
the first flag there.

Test: m
Bug: 276752881
(cherry picked from https://googleplex-android-review.googlesource.com/q/commit:5fc9dc6c0e9a121dd3556fd918088dbb14970af6)
Merged-In: I81b8f4f42bafc1adee139b35cc111dc852c4d2a2

Change-Id: I81b8f4f42bafc1adee139b35cc111dc852c4d2a2

AconfigFlags.bp

@@ -18,6 +18,7 @@ java_defaults {
 
     // Add java_aconfig_libraries to here to add them to the core framework
     srcs: [
+        ":android.os.flags-aconfig-java{.generated_srcjars}",
         ":android.security.flags-aconfig-java{.generated_srcjars}",
         ":com.android.hardware.camera2-aconfig-java{.generated_srcjars}",
         ":com.android.window.flags.window-aconfig-java{.generated_srcjars}",
@@ -88,6 +89,19 @@ java_aconfig_library {
     defaults: ["framework-minus-apex-aconfig-java-defaults"],
 }
 
+// OS
+aconfig_declarations {
+    name: "android.os.flags-aconfig",
+    package: "android.os",
+    srcs: ["core/java/android/os/*.aconfig"],
+}
+
+java_aconfig_library {
+    name: "android.os.flags-aconfig-java",
+    aconfig_declarations: "android.os.flags-aconfig",
+    defaults: ["framework-minus-apex-aconfig-java-defaults"],
+}
+
 // Security
 aconfig_declarations {
     name: "android.security.flags-aconfig",

core/java/android/os/flags.aconfig

+package: "android.os"
+
+flag {
+    name: "disallow_cellular_null_ciphers_restriction"
+    namespace: "cellular_security"
+    description: "Guards a new UserManager user restriction that admins can use to require cellular encryption on their managed devices."
+    bug: "276752881"
+}