Set min_sdk_version to be part of mainline modules

Modules contributing mainline modules (APK/APEX) should set
min_sdk_version as well as apex_available.

For now setting min_sdk_version doesn't change build outputs.
But build-time checks will be added soon.

Bug: 152655956
Test: m
Merged-In: I921b3575734c2b30840179910e5a3d8153d9dd06
Change-Id: I921b3575734c2b30840179910e5a3d8153d9dd06
(cherry picked from commit e42850f4b8b1ad38f526c494db07259aeb09f8a0)
diff --git a/libflags/Android.bp b/libflags/Android.bp
index 81032f1..2295595 100644
--- a/libflags/Android.bp
+++ b/libflags/Android.bp
@@ -15,6 +15,7 @@
         "//apex_available:platform",
         "com.android.resolv",
     ],
+    min_sdk_version: "29",
 }
 
 // Tests
@@ -27,7 +28,7 @@
         "-Wextra",
     ],
     srcs: [
-        "server_configurable_flags_test.cc"
+        "server_configurable_flags_test.cc",
     ],
     shared_libs: [
         "server_configurable_flags",