Add `--all` for exiting all active validators

[KaloyanTanev]

🎯 Problem to be solved

Currently if we want to exit all active validators in the cluster, it is quite cumbersome process, having to specify every validator's PK or index. Having big number of validators (i.e.: 1000) makes this quite slow. It would be great if users can simply add --all flag and exit all active validators.

🛠️ Proposed solution

• [x] Add --all flag to available flags for the exit command
• [x] Add --all for exit sign command
• [x] Add --all for exit broadcast command
• [x] Add --all for exit fetch command

🧪 Tests

• [x] Tested by new automated unit tests
• [x] Manually tested on local Kurtosis devnet
• [ ] Manually tested on test Holesky clusters

❌ Out of Scope

Exiting all validators using the VC. This ticket is only about implementing this for charon exits.