SignerSource: rename input scheme to prompt, default to bip44 solana base key (#17154)

* Rename ask to prompt

* Default to Solana bip44 base if no derivation-path

* Add SignerSource legacy field, support legacy ASK

* Update docs

* Fix docs: validator current doesn't support uri SignerSources

docs/src/running-validator/validator-start.md

@@ -155,7 +155,7 @@ solana-keygen new --no-outfile
 The corresponding identity public key can now be viewed by running:
 
 ```bash
-solana-keygen pubkey ask://
+solana-keygen pubkey ASK
 ```
 
 and then entering your seed phrase.
@@ -294,7 +294,7 @@ The ledger will be placed in the `ledger/` directory by default, use the
 > [paper wallet seed phrase](../wallet-guide/paper-wallet.md)
 > for your `--identity` and/or
 > `--authorized-voter` keypairs. To use these, pass the respective argument as
-> `solana-validator --identity ask:// ... --authorized-voter ask:// ...`
+> `solana-validator --identity ASK ... --authorized-voter ASK ...`
 > and you will be prompted to enter your seed phrases and optional passphrase.
 
 Confirm your validator connected to the network by opening a new terminal and