Merge bitcoin/bitcoin#32429: docs: Improve keypoolrefill RPC docs

ff35a4b docs: Improve `keypoolrefill` RPC docs (w0xlt)

Pull request description:

  Update `keypoolrefill` RPC docs to make it clear that descriptor wallets have 4 ScriptPubKeyManagers by default and each of them is updated in this command, as suggested bitcoin/bitcoin#29924 (comment)

  Closes bitcoin/bitcoin#29924

ACKs for top commit:
  achow101:
    ACK ff35a4b
  brunoerg:
    code review ACK ff35a4b

Tree-SHA512: b6b9abe3fecebf9551b4ce9280794292c6ac44ccaeb2b9d60eeb4b2c177fe8372d0fe103f99c9cc0baeb2559ec019d1c495c233f24a600531153a38eeacb9670

Author: achow101

src/wallet/rpc/addresses.cpp

@@ -214,7 +214,8 @@ RPCHelpMan listaddressgroupings()
 RPCHelpMan keypoolrefill()
 {
     return RPCHelpMan{"keypoolrefill",
-                "\nFills the keypool."+
+                "Refills each descriptor keypool in the wallet up to the specified number of new keys.\n"
+                "By default, descriptor wallets have 4 active ranged descriptors (\"legacy\", \"p2sh-segwit\", \"bech32\", and \"bech32m\"), each with " + util::ToString(DEFAULT_KEYPOOL_SIZE) + " entries.\n" +
         HELP_REQUIRING_PASSPHRASE,
                 {
                     {"newsize", RPCArg::Type::NUM, RPCArg::DefaultHint{strprintf("%u, or as set by -keypool", DEFAULT_KEYPOOL_SIZE)}, "The new keypool size"},