Add option to importmulti add an imported pubkey to the keypool

Adds a new option to importmulti where the pubkeys specified in the import
object can be added to the keypool. This only works if the wallet has
private keys disabled.

src/wallet/rpcdump.cpp

@@ -1207,6 +1207,12 @@ static UniValue ProcessImport(CWallet * const pwallet, const UniValue& data, con
             throw JSONRPCError(RPC_INVALID_PARAMETER, "Internal addresses should not have a label");
         }
         const std::string& label = data.exists("label") ? data["label"].get_str() : "";
+        const bool add_keypool = data.exists("keypool") ? data["keypool"].get_bool() : false;
+
+        // Add to keypool only works with privkeys disabled
+        if (add_keypool && !pwallet->IsWalletFlagSet(WALLET_FLAG_DISABLE_PRIVATE_KEYS)) {
+            throw JSONRPCError(RPC_INVALID_PARAMETER, "Keys can only be imported to the keypool when private keys are disabled");
+        }
 
         ImportData import_data;
         std::map<CKeyID, CPubKey> pubkey_map;
@@ -1267,6 +1273,11 @@ static UniValue ProcessImport(CWallet * const pwallet, const UniValue& data, con
                 pwallet->AddKeyOrigin(pubkey, key_orig_it->second);
             }
             pwallet->mapKeyMetadata[id].nCreateTime = timestamp;
+
+            // Add to keypool only works with pubkeys
+            if (add_keypool) {
+                pwallet->AddKeypoolPubkey(pubkey, internal);
+            }
         }
 
         for (const CScript& script : script_pub_keys) {