Merge #10757: RPC: Introduce getblockstats to plot things

41d0476f62 Tests: Add data file (Anthony Towns)
4cbfb6aad9 Tests: Test new getblockstats RPC (Jorge Timón)
35e77a0288 RPC: Introduce getblockstats (Jorge Timón)
cda8e36f01 Refactor: RPC: Separate GetBlockChecked() from getblock() (Jorge Timón)

Pull request description:

  It returns per block statistics about several things. It should be easy to add more if people think of other things to add or remove some if I went too far (but once written, why not keep it? EDIT: answer: not to test or maintain them).

  The currently available options are: minfee,maxfee,totalfee,minfeerate,maxfeerate,avgfee,avgfeerate,txs,ins,outs (EDIT: see updated list in the rpc call documentation)

  For the x axis, one can use height or block.nTime (I guess I could add mediantime if there's interest [EDIT: nobody showed interest but I implemented mediantime nonetheless, in fact there's no distinction between x or y axis anymore, that's for the caller to judge]).

  To calculate fees, -txindex is required.

Tree-SHA512: 2b2787a3c7dc4a11df1fce62c8a4c748f5347d7f7104205d5f0962ffec1e0370c825b49fd4d58ce8ce86bf39d8453f698bcd46206eea505f077541ca7d59b18c

test/functional/test_runner.py

@@ -135,6 +135,7 @@ BASE_SCRIPTS = [
     'wallet_resendwallettransactions.py',
     'wallet_fallbackfee.py',
     'feature_minchainwork.py',
+    'rpc_getblockstats.py',
     'p2p_fingerprint.py',
     'feature_uacomment.py',
     'p2p_unrequested_blocks.py',