Add ability to ignore `SCRIPT_VERIFY_DISCOURAGE_x` flags when broadcasting transactions on test networks.

After bugs like: https://github.com/btcsuite/btcd/issues/1906 it would be useful to be able to reproduce these bugs in regtest. Currently to do so you would need to manually edit the code and comment out the script flag, then compile your self. It would be beneficial if we could disable these flags to create more reproducible tests.