refactor: move run_command from util to common

Quoting ryanofsky: "util can be the library for things included in the kernel
which the kernel can depend on, and common can be the library for other code
that needs to be shared internally, but should not be part of the kernel or
shared externally."

src/common/run_command.h

@@ -0,0 +1,21 @@
+// Copyright (c) 2022 The Bitcoin Core developers
+// Distributed under the MIT software license, see the accompanying
+// file COPYING or http://www.opensource.org/licenses/mit-license.php.
+
+#ifndef BITCOIN_COMMON_RUN_COMMAND_H
+#define BITCOIN_COMMON_RUN_COMMAND_H
+
+#include <string>
+
+class UniValue;
+
+/**
+ * Execute a command which returns JSON, and parse the result.
+ *
+ * @param str_command The command to execute, including any arguments
+ * @param str_std_in string to pass to stdin
+ * @return parsed JSON
+ */
+UniValue RunCommandParseJSON(const std::string& str_command, const std::string& str_std_in="");
+
+#endif // BITCOIN_COMMON_RUN_COMMAND_H