Move (contain) contracts under './contracts'

[krebernisak]

We did this for Solana where all contract project files were moved from root to ./contracts. One of the benefits is that we separate the yarn.lock for contracts from the root one (monorepo), and it's a cleaner setup in general.

The programs themselves were moved under ./contracts/programs as they have the domain name of programs on Solana. Here we could move it under ./contracts/contracts, ./contracts/cw or similar.