Allow result submission to origin daemon with self-select

With `self-select` mode enabled, the `submit-to-origin` config option
will let the `SelfSelectClient` submit the solution to both
the daemon where it got the template from as well as to
the connected pool, for miners that want to do pool minining
with Monero and solo mining with an altcoin (merged mining variant).

Thank you and special credit to @StriderDM (https://github.com/StriderDM)!

src/base/net/stratum/Pool.h

@@ -72,6 +72,7 @@ public:
     static const char *kPass;
     static const char *kRigId;
     static const char *kSelfSelect;
+    static const char* kSubmitToOrigin;
     static const char *kSOCKS5;
     static const char *kTls;
     static const char *kUrl;
@@ -156,6 +157,7 @@ private:
     uint64_t m_pollInterval         = kDefaultPollInterval;
     Url m_daemon;
     Url m_url;
+    bool m_submit_to_origin         = false;
 
 #   ifdef XMRIG_FEATURE_BENCHMARK
     std::shared_ptr<BenchConfig> m_benchmark;