EIP-747: Add wallet_watchAsset

I would be nice to have this functionality like Metamask. You can add a custom ERC20 token.

```
window.ethereum.request({
method: "wallet_watchAsset",
params: {
type: "ERC20", // Initially only supports ERC20, but eventually more!
options: {
address: "0xc2768beF7a6BB57F0FfA169a9ED4017c09696FF1", // The address that the token is at.
symbol: "PE", // A ticker symbol or shorthand, up to 5 chars.
decimals: 6, // The number of decimals in the token
image: "https://raw.githubusercontent.com/peronio-ar/branding/main/logo/256.png", // A string url of the token logo
},
}
```