Add an integration test for mainline beta prod mode codegen

1, update the configuration to include a mockup beta namespace.
2, create mockup mainline beta flags using the mockup beta namespace
3, added test points to lock down mainline beta codegen

Bug: b/406508083
Test: atest -c
Change-Id: Id23689383c9fe48d01ab6e4262dc4ccc1254373d