Merge #11099: [RPC][mempool]: Add savemempool RPC

1aa97ee08 Add savemempool RPC (Lawrence Nahum)
467cbbcbf Add return value to DumpMempool (Lawrence Nahum)

Pull request description:

  Adds a simple parameterless rpc command to dump the mempool.

  Rationale:

  Sometimes there can be a crash for whatever reason (bug, power loss, etc) causing the mempool.dat file to not be saved.

  This change allows to script/cron the rpc call to have more regular saves to the file as well as cli/ad-hoc.

  This should solve issue https://github.com/bitcoin/bitcoin/issues/11086

Tree-SHA512: e856ae9777425a4521279c9b58e69285d8e374790bebefd3284cf91931eac0e456f86224f427a087a01bf70440bf6e439fa02c8a34940eb1046ae473e98b6aaa

src/validation.h

@@ -478,7 +478,7 @@ static const unsigned int REJECT_HIGHFEE = 0x100;
 CBlockFileInfo* GetBlockFileInfo(size_t n);
 
 /** Dump the mempool to disk. */
-void DumpMempool();
+bool DumpMempool();
 
 /** Load the mempool from disk. */
 bool LoadMempool();