Keep alive hotkey accounts that drop below ED

[orriin]

Hotkey accounts frequently drop below the ED when they move funds to their coldkey, causing the accounts to get reaped.

This currently has no negative behavior as the accounts are just recreated the next time the hotkey interacts with the chain, but it's best that this doesn't happen.

To resolve this, we need to increment the providers for hotkey accounts that have an associated coldkey account. This will prevent the account from being reaped when its value drops below the ED (https://github.com/paritytech/polkadot-sdk/blob/0ae721970909efc3b2a049632c9c904d9fa4fed1/substrate/frame/system/src/lib.rs#L2218).