Merge bitcoin/bitcoin#30525: doc, rpc : #30275 followups

fa2f26960e [rpc, fees]: add more detail on the fee estimation modes (ismaelsadeeq)
6e7e620864 [doc]: add `30275` release notes (ismaelsadeeq)

Pull request description:

  This PR:
  1. Adds release notes for #30275
  2. Describe fee estimation modes in RPC help texts

ACKs for top commit:
  achow101:
    ACK fa2f26960e
  glozow:
    ACK fa2f26960e
  willcl-ark:
    ACK fa2f26960e
  tdb3:
    re ACK fa2f26960e

Tree-SHA512: b8ea000b599297b954dc770137c29b47153e68644c58550a73e34b74ecb8b65e78417875481efdfdf6aab0018a9cd1d90d8baa5a015e70aca0975f6e1dc9598c

src/rpc/fees.cpp

@@ -23,7 +23,7 @@
 #include <string>
 
 using common::FeeModeFromString;
-using common::FeeModes;
+using common::FeeModesDetail;
 using common::InvalidEstimateModeErrorMessage;
 using node::NodeContext;
 
@@ -37,12 +37,7 @@ static RPCHelpMan estimatesmartfee()
         {
             {"conf_target", RPCArg::Type::NUM, RPCArg::Optional::NO, "Confirmation target in blocks (1 - 1008)"},
             {"estimate_mode", RPCArg::Type::STR, RPCArg::Default{"economical"}, "The fee estimate mode.\n"
-            "Whether to return a more conservative estimate which also satisfies\n"
-            "a longer history. A conservative estimate potentially returns a\n"
-            "higher feerate and is more likely to be sufficient for the desired\n"
-            "target, but is not as responsive to short term drops in the\n"
-            "prevailing fee market. Must be one of (case insensitive):\n"
-             "\"" + FeeModes("\"\n\"") + "\""},
+              + FeeModesDetail(std::string("default mode will be used"))},
         },
         RPCResult{
             RPCResult::Type::OBJ, "", "",