Implement add validators multi command

[dB2510]

🎯 Problem to be solved

We have implemented the charon alpha add-validators-solo command (#1887), which allows a solo operator to add validators to a cluster. However, we now need to enhance this functionality to support the addition of validators by multiple operators in a distributed manner. The new command will resemble charon dkg as it will be executed simultaneously by all cluster operators.

🛠️ Proposed solution

• [x] Approved design doc: link
• [x] Core team consensus on the proposed solution

Create a new command: charon alpha add-validators-multi

• It takes a legacy lock file as input
• It takes withdrawal addresses and fee_recipients as input
• It generates keys
• It generates a new cluster state file with the legacy_lock and add_validators mutations

This command will re-use a lot of the current DKG functionality, but instead of generating a legacy cluster lock, it will generate the above mentioned mutable cluster lock containing the legacy_lock/v1.7.0 and add_validators/v0.0.1 mutations.

[boulder225]

to discuss @OisinKyne @xenowits