[wip]: Exit transaction generation

[valefar-on-discord]

Preliminary implementation of exit transaction creation.

Because my staking-cli PR is still in review, I have copied a local version of it in this pr in a separate commit. Hopefully that can be landed soon.

To test this:

• Create some keystores
• Go through the new Generate a pre-signed exit transaction (I'm going to change that wording)
• Select the folder that contains the keystores
• Provide the necessary information (master password, epoch, and validator index for each keystore) [I think the best way to handle a lot of files here is scrolling. I messed up the height of the element so more than 3 keystores will cause an overflow issue but I am going to fix that in the morning]
• Choose the location where the exit transactions will be stored (There is a problem here that I am going to resolve in the CLI)
• Creation will take a minute
• Hopefully it worked

Again, this is not the final form but the very first iteration. Looking for any and all feedback and I'll be improving it tomorrow by fixing UX issues and improving error handling.

I apologize for being overly enthusiastic with my code modifications outside of this feature

Time to 😴

[remyroy]

I'll hold off on reviewing this further until there is more progress and a resolution with https://github.com/ethereum/staking-deposit-cli/pull/355

[valefar-on-discord]

https://github.com/ethereum/staking-deposit-cli/pull/355#issuecomment-1886062085