Move Transaction Builder to this monorepo

[katspaugh]

Transaction Builder txs are the third most popular transaction type:

When we add a new supported chain, Tx Builder is always enabled. However, Tx Builder depends on safe-deployments for chain support, so it has to be updated every time. It's currently part of this repo – https://github.com/safe-global/safe-react-apps – with its own release process.

We should migrate it to this repo and share the same version of safe-deployments as the Wallet web app.