Support changing password of alias key

[v9n]

We should support changing password of alias key or bls key to make it easy to rotate the password.

Second option to consider is do this outside of our AVS code, which maybe a better option to avoid expose the original password to AVS. We need to define a clear and simple step by step guide

[chrisli30]

I believe many operator/validator documentations already have similar setups that we could emulate. For example, RocketPool has excellent "securing your node" instructions, which we could replicate on our /docs pages. (but it’s not for BLS password)
Reference: https://oak-network.atlassian.net/browse/ENG-762