Update new wasm hash naming to expected new_wasm_hash

[pselle]

What

The argument to upgrade should be new_wasm_hash, not wasm_hash, as this is what we're standardizing on per https://developers.stellar.org/docs/build/guides/conventions/upgrading-contracts.

Why

Scaffold Stellar assumes new_wasm_hash when upgrading contracts, so this function should use that argument.

[chadoh]

Seems like the right thing to do to me! @willemneal any comments here?

[willemneal]

An the low level contract invoke the name doesn't matter, since the args are just a vec. So we should update Scaffold stellar to just pass a the bytesN<32>. But completely agree we should use the same name in the official trait!!