Merge bitcoin#28980: rpc: encryptwallet help, mention HD seed rotation and backup requirement

ca09415 rpc, doc: encryptwallet, mention HD seed rotation and new backup (furszy)

Pull request description:

  Small and simple PR, updating the `encryptwallet` help message.

  Better to notify users about the HD seed rotation and the new
  backup requirement before executing the encryption process.
  Ensuring they are prepared to update previous backups and
  securely safeguard the updated wallet file.

ACKs for top commit:
  S3RK:
    ACK ca09415
  achow101:
    ACK ca09415

Tree-SHA512: f0ee65f5cea66450566e3a85e066d4c06b3293dd0e0b2ed5fafdb7fb11da0a2cd94407299a3c57a0706c2ed782f8eabb73443e85d8099a62a3fb10a02636ab46

Author: achow101

src/wallet/rpc/encrypt.cpp

@@ -220,7 +220,11 @@ RPCHelpMan encryptwallet()
                 "After this, any calls that interact with private keys such as sending or signing \n"
                 "will require the passphrase to be set prior the making these calls.\n"
                 "Use the walletpassphrase call for this, and then walletlock call.\n"
-                "If the wallet is already encrypted, use the walletpassphrasechange call.\n",
+                "If the wallet is already encrypted, use the walletpassphrasechange call.\n"
+                "** IMPORTANT **\n"
+                "For security reasons, the encryption process will generate a new HD seed, resulting\n"
+                "in the creation of a fresh set of active descriptors. Therefore, it is crucial to\n"
+                "securely back up the newly generated wallet file using the backupwallet RPC.\n",
                 {
                     {"passphrase", RPCArg::Type::STR, RPCArg::Optional::NO, "The pass phrase to encrypt the wallet with. It must be at least 1 character, but should be long."},
                 },
@@ -266,7 +270,7 @@ RPCHelpMan encryptwallet()
     if (pwallet->IsHDEnabled()) {
         return "wallet encrypted; If you forget the passphrase, you will lose access to your funds. Make sure that you have backup of your seed or mnemonic.";
     }
-    return "wallet encrypted; The keypool has been flushed. You need to make a new backup.";
+    return "wallet encrypted; The keypool has been flushed. You need to make a new backup with the backupwallet RPC.";
 },
     };
 }