Add RPC options for RBF, confirmation target, and conservative fee estimation.

Add support for setting each of these attributes on a per RPC call basis to sendtoaddress, sendmany, fundrawtransaction (already had RBF), and bumpfee (already had RBF and conf target).

src/policy/fees.cpp

@@ -36,6 +36,20 @@ std::string StringForFeeReason(FeeReason reason) {
     return reason_string->second;
 }
 
+bool FeeModeFromString(const std::string& mode_string, FeeEstimateMode& fee_estimate_mode) {
+    static const std::map<std::string, FeeEstimateMode> fee_modes = {
+        {"UNSET", FeeEstimateMode::UNSET},
+        {"ECONOMICAL", FeeEstimateMode::ECONOMICAL},
+        {"CONSERVATIVE", FeeEstimateMode::CONSERVATIVE},
+    };
+    auto mode = fee_modes.find(mode_string);
+
+    if (mode == fee_modes.end()) return false;
+
+    fee_estimate_mode = mode->second;
+    return true;
+}
+
 /**
  * We will instantiate an instance of this class to track transactions that were
  * included in a block. We will lump transactions into a bucket according to their