Add support for rETH handling

[RomiRand]

Even though rETH is not primarily targeted at node operators, it might be convenient to also support dealing with our LSD via the smartnode stack. So I would like to add the ability to stake/unstake ETH by swapping it to/from rETH. The minimal solution would use the deposit pool only, but if deemed useful I'd also add other popular options like Uniswap.

I would love to hear if such a feature would be desired. If yes, I'd also be thankful for feedback (especially "naming things" has proven to be one of my weaknesses).

Progress:

• [x] stake via deposit pool
• [ ] unstake via deposit pool
• [ ] stake via uniswap/1inch/etc. (?)
• [ ] unstake via uniswap/1inch/etc.(?)