fix: use right admin priv key for register subnet script

[sebastiendan]

Description

This PR fixes the issue introduced by #107 where a single private key is used both for creating the admin wallet capable of register a new subnet and the new subnet id. To fix this, we introduce a new arg to pass an adminPrivateKey separately from the sequencerPrivateKey.

Passing e2e-tests workflow run

PR Checklist:

• I have performed a self-review of my code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• I have added or updated tests that comprehensively prove my change is effective or that my feature works