Merge #6452: fix: store ready queues on the mixing masternode

24dcce979b fix: store ready queues on the mixing masternode (UdjinM6)

Pull request description:

  ## Issue being fixed or feature implemented
  We normally do not re-relay/store "ready" `dsq`-s because these are ment to be relayed between mixing clients and the mixing masternode only. I works ok when you simply send `dsq` messages because no extra steps are required. However since 70235 we send `dsq` _`inv`-s_ first and we send actual `dsq`-s only if they are requested via `getdata`. The problem here is that `ProcessGetData()` queries `vecCoinJoinQueue` via `GetQueueFromHash()` to get the data to send back but there is none because we never saved it.

  ## What was done?

  ## How Has This Been Tested?
  To test this patch you need a MN but you can test 2 cases _without this patch_ to indirectly test the idea:
  1. try mixing on develop: almost no mixing txes, maybe 10 or so in an hour if you are lucky to mix on an old MN that often
  2. ignore old MNs (`MIN_PEER_PROTO_VERSION = 70235`): 0 mixing txes, no matter how long you wait
  3. pretend being an old client to receive no-inv `dsq` only (`PROTOCOL_VERSION = 70233`): no issues, mixing on these nodes is as fast as usual, several txes per block (need a couple of nodes like that on the network so that a mixing session could be completed, I'm running one node for now so that anyone could join and test it)

  I'm running a testnet MN with this fix and applied "ignore old mn" patch on my local machine. Local wallet got mixing tx when it finally hit the patched mn. Also confirmed this via MN`debug.log` (`Create`/`Relay`/`CommitFinalTransaction` in logs).

  ## Breaking Changes

  ## Checklist:
  - [ ] I have performed a self-review of my own code
  - [ ] I have commented my code, particularly in hard-to-understand areas
  - [ ] I have added or updated relevant unit/integration/functional/e2e tests
  - [ ] I have made corresponding changes to the documentation
  - [ ] I have assigned this pull request to a milestone _(for repository code-owners and collaborators only)_

ACKs for top commit:
  PastaPastaPasta:
    utACK 24dcce979b

Tree-SHA512: 69cee5401d26eec3f66166a754b8020e7f550dac4a0fdea8ec48ea1082f1286e647ac0a26a189c4d39e1a9da4e7ac36f71913684b13ea0fb4b3cfe831174970e

src/coinjoin/server.cpp

@@ -520,6 +520,7 @@ void CCoinJoinServer::CheckForCompleteQueue()
                                      "with %d participants\n", dsq.ToString(), vecSessionCollaterals.size());
         dsq.Sign(*m_mn_activeman);
         m_peerman->RelayDSQ(dsq);
+        WITH_LOCK(cs_vecqueue, vecCoinJoinQueue.push_back(dsq));
     }
 }