Proxy to only transfer free balance.

[JuanCortez93]

Is your feature request related to a problem? Please describe.

I have funds on a wallet, the entire balance is staked. I would like to have a way to access to the free_balance with a new proxy that only can transfer TAO from an account to another.

With this proxy users can have a wallet protected by 2 proxies : an staking proxy and the proxy proposed. The second proxy cannot unstake, and the first cannot send free balance to another wallet.

Describe the solution you'd like

The solution is to code a custom proxy, because it is not one of the default proxy types.

Describe alternatives you've considered

No response

Additional context

No response

[camfairchild]

Implemented in #723