Merge bitcoin#23021: net: switch to signet DNS seed

dc10ca3 net: switch to signet DNS seed (Sjors Provoost)

Pull request description:

  I spun up a DNS seed for Signet, source: sipa/bitcoin-seeder#94

  If anyone else spins up a DNS seed, let me know in the comment and I'll add it.

  Because one DNS seed is not very diverse, this PR leaves two hardcoded nodes just in case (). The one dropped node no longer exists.

  Replaces bitcoin#23000.

ACKs for top commit:
  kallewoof:
    utACK dc10ca3
  laanwj:
    Concept and code review ACK dc10ca3
  jarolrod:
    ACK dc10ca3
  shaavan:
    ACK dc10ca3

Tree-SHA512: 534d189becd51974042fddc3efe3df230484f05cd945e756eaf6a4a8a580e2161b3a959eb3d44dea526269eea6f87a033f7cbfe86586782c6ca4ee7c7c4097a9

Author: laanwj

src/chainparams.cpp

@@ -280,8 +280,10 @@ class SigNetParams : public CChainParams {
 
         if (!args.IsArgSet("-signetchallenge")) {
             bin = ParseHex("512103ad5e0edad18cb1f0fc0d28a3d4f1f3e445640337489abb10404f2d1e086be430210359ef5021964fe22d6f8e05b2463c9540ce96883fe3b278760f048f5189f2e6c452ae");
+            vSeeds.emplace_back("seed.signet.bitcoin.sprovoost.nl");
+
+            // TODO: remove hardcoded nodes once there are more DNS seeds
             vSeeds.emplace_back("178.128.221.177");
-            vSeeds.emplace_back("2a01:7c8:d005:390::5");
             vSeeds.emplace_back("v7ajjeirttkbnt32wpy3c6w3emwnfr3fkla7hpxcfokr3ysd3kqtzmqd.onion:38333");
 
             consensus.nMinimumChainWork = uint256S("0x0000000000000000000000000000000000000000000000000000008546553c03");