wallet-core: implement EIP2333 key derivation

[fed-franz]

Summary

Implement the EIP2333 derivation scheme as an internal library to be used by the existing key generator

Possible solution design or implementation

Implement methods described in the specification document

Additional context

The implementation will follow EIP2333 specs and use the following external implementations as a secondary reference:

• https://github.com/ethereum/staking-deposit-cli (Ethereum reference implementation)
• https://github.com/maidsafe/sn_rust_bls_derivation (compliant implementation in Rust)

Once EIP2333 derivation has been implemented, it will be possible to adhere to EIP2334 by deriving keys with the appropriate derivation path