Add a couple of example contracts to aztec.js

[PhilWindle]

So that external devs are not forced to yarn add global @aztec/noir-contracts and then reference a contract buried deep within node's global repo we should add a couple of example contracts directly to aztec.js and have them nicely exported.

[spypsy]

updated requirement:
Add the example contracts to aztec-cli but not aztec.js as it's quite complex to do atm, given noir-contracts package is dependent on aztec.js