Option to change key_management_mode in multitenancy wallets

[DaevMithran]

Currently acapy allows the option to choose key management mode only during a sub-wallet creation

• We should also support an option to change the key_management mode in acapy according to the user's need.

• Using update_wallet method, user can create a new wallet_key and then use the wallet as an unmanaged wallet.

• This also allows a user to export managed wallets and use it as a separate wallet