External OZ dependency is not needed

[julien-devatom]

The oz contracts submodule imports an ERC20 for the MockERC20 contract.

So it enforces the use of forge to work with blue where the dependency is not so used except for testing.

Without it, we can easily publish Morpho to npm and allow hardhat-only setup, without enforcing the foundry tool for all integrators.

Since the dependency is used only for testing purposes, I suggest coding a custom erc20 (really easy to do) and adding a CI to publish blue to npm.

[Rubilmax]

I'm ok with it

[MerlinEgalite]

No problem on my side as well