## Description 

add a cli tool to convert between sui keystore format (base64 of 33 byte
flag || private key) vs the wallet format (hex of 32 byte private key).

## Test Plan 

```
target/debug/sui keytool convert ABTk0pAIhn4GylSCKycYx+7ItEQim0h6ohIqVmZdRX8C 

2023-04-18T15:33:22.742744Z  INFO sui::keytool: Wallet formatted private key: 0x14e4d29008867e06ca54822b2718c7eec8b444229b487aa2122a56665d457f02

target/debug/sui keytool convert 0x14e4d29008867e06ca54822b2718c7eec8b444229b487aa2122a56665d457f02

2023-04-18T15:33:33.572271Z  INFO sui::keytool: Keystore formatted private key: "ABTk0pAIhn4GylSCKycYx+7ItEQim0h6ohIqVmZdRX8C"
```
---
If your changes are not user-facing and not a breaking change, you can
skip the following section. Otherwise, please indicate what changed, and
then add to the Release Notes section as highlighted during the release
process.

### Type of Change (Check all that apply)

- [ ] user-visible impact
- [ ] breaking change for a client SDKs
- [ ] breaking change for FNs (FN binary must upgrade)
- [ ] breaking change for validators or node operators (must upgrade
binaries)
- [ ] breaking change for on-chain data layout
- [ ] necessitate either a data wipe or data migration

### Release notes