chore: update .CODEOWNERS for the DeFi team

[gregorydemay]

Update the codeowner file to reflect the merge of the cross-chain and FI teams into a single DeFi team. Everything that was owned by @dfinity/cross-chain-team and @dfinity/finint is now owned by @dfinity/defi-team.

[marc0olo]

@gregorydemay we also need to decide how to deal with examples where dfinity/growth is codeowner. I am wondering if the defi team should also take ownership over all the ICP / token relevant examples.

here the full list of potentially relevant examples:

/hosting/oisy-signer-demo/ @dfinity/growth

/motoko/ic-pos/ @dfinity/growth
/motoko/icp_transfer/ @dfinity/growth
/motoko/icrc2-swap/ @dfinity/growth
/motoko/nft-creator/ @dfinity/growth
/motoko/token_transfer/ @dfinity/growth
/motoko/token_transfer_from/ @dfinity/growth


/rust/icp_transfer/ @dfinity/growth
/rust/token_transfer/ @dfinity/growth
/rust/token_transfer_from/ @dfinity/growth

[gregorydemay]

Hi @marc0olo ! We will discuss it in our team meeting and come back to you.