fix: make keys command more intuitive

[AaronCQL]

Changes

Generate a new key:

jup keys add <name>

Import from a JSON file generated via solana-keygen:

jup keys add <name> --file /path/to/solana-keygen.json

Import from private key or seed phrase:

jup keys add <name> --seed-phrase "word1 word2 ..."
jup keys add <name> --seed-phrase "word1 word2 ..." --derivation-path "m/44'/501'/0'/0'" # optional, defaults to "m/44'/501'/0'/0'"
jup keys add <name> --private-key <key> # accepts hex, base58, base64, or a JSON byte array

---

Closes #4

[cavemanloverboy]

fan of this