Merge bitcoin/bitcoin#22722: rpc: update estimatesmartfee to return max of CBlockPolicyEstimator::estimateSmartFee, mempoolMinFee and minRelayTxFee

ea31caf6b4 update estimatesmartfee rpc to return max of estimateSmartFee, mempoolMinFee and minRelayTxFee. (pranabp-bit)

Pull request description:

  This PR is in response to the issue [#19699](https://github.com/bitcoin/bitcoin/issues/19699).

  Based on the discussion in the comments of PR [#22673](https://github.com/bitcoin/bitcoin/pull/22673) changes have been made in the `estimatesmartfee` itself such that it takes into account `mempoolMinFee` and `relayMinFee` . Hence it provides a fee estimate that is most likely to be paid by the user in an actual transaction, preventing issues such as [#16072](https://github.com/bitcoin/bitcoin/issues/16072).

  The test file test/functional/feature_fee_estimation.py has also been updated to check this functionality.

ACKs for top commit:
  meshcollider:
    re-utACK ea31caf6b4

Tree-SHA512: 8f36153a07cbd552c5c13d11d9c6e987a7a555ea4cc83f2573c0c92dd97c706d90c30a7248671437c2f3a836d3272f8fad53d15a5fa6efaa0409ae8009b0a18d

test/functional/feature_fee_estimation.py

@@ -132,9 +132,13 @@ def check_smart_estimates(node, fees_seen):
     delta = 1.0e-6  # account for rounding error
     last_feerate = float(max(fees_seen))
     all_smart_estimates = [node.estimatesmartfee(i) for i in range(1, 26)]
+    mempoolMinFee = node.getmempoolinfo()['mempoolminfee']
+    minRelaytxFee = node.getmempoolinfo()['minrelaytxfee']
     for i, e in enumerate(all_smart_estimates):  # estimate is for i+1
         feerate = float(e["feerate"])
         assert_greater_than(feerate, 0)
+        assert_greater_than_or_equal(feerate, float(mempoolMinFee))
+        assert_greater_than_or_equal(feerate, float(minRelaytxFee))
 
         if feerate + delta < min(fees_seen) or feerate - delta > max(fees_seen):
             raise AssertionError(f"Estimated fee ({feerate}) out of range ({min(fees_seen)},{max(fees_seen)})")
@@ -275,6 +279,12 @@ class EstimateFeeTest(BitcoinTestFramework):
         self.log.info("Final estimates after emptying mempools")
         check_estimates(self.nodes[1], self.fees_per_kb)
 
+        # check that the effective feerate is greater than or equal to the mempoolminfee even for high mempoolminfee
+        self.log.info("Test fee rate estimation after restarting node with high MempoolMinFee")
+        high_val = 3*self.nodes[1].estimatesmartfee(1)['feerate']
+        self.restart_node(1, extra_args=[f'-minrelaytxfee={high_val}'])
+        check_estimates(self.nodes[1], self.fees_per_kb)
+
         self.log.info("Testing that fee estimation is disabled in blocksonly.")
         self.restart_node(0, ["-blocksonly"])
         assert_raises_rpc_error(-32603, "Fee estimation disabled",