Add key details function

[AyushBherwani1998]

As of now, getKeyDetails function is missing which is present in Web implementation.

Docs: https://web3auth.io/docs/sdk/core-kit/mpc-core-kit/usage#get-user-info

[metalurgical]

Added in #21

[AyushBherwani1998]

The function is working fine, but it's not aligned with Web SDK. https://web3auth.io/docs/sdk/core-kit/mpc-core-kit/usage#returns-1

We should at least update the shareDescriptions which returns String instead of Dictionary.

[metalurgical]

This was part of #30