Allow secure keypair input for solana-validator cli (#7080)

* Allow secure keypair input for solana-validator cli

* feedback

* Add --skip-mnemonic-validation

* Update --identity to --identity-keypair

* Use struct instead of tuple

* Fix dependencies

* cargo fmt

* Add basic tests

* Use `seed phrase` instead of `mnemonic`

* Update passphrase prompt

multinode-demo/bootstrap-leader.sh

@@ -76,10 +76,10 @@ ledger_dir="$SOLANA_CONFIG_DIR"/bootstrap-leader
 args+=(
   --accounts "$SOLANA_CONFIG_DIR"/bootstrap-leader/accounts
   --enable-rpc-exit
-  --identity "$identity_keypair"
   --ledger "$ledger_dir"
   --rpc-port 8899
   --snapshot-interval-slots 100
+  --identity-keypair "$identity_keypair"
   --storage-keypair "$storage_keypair"
   --voting-keypair "$vote_keypair"
   --rpc-drone-address 127.0.0.1:9900