feat: Limit cache loading in cluster (#2985)

This PR adds an option to limit simultaneous cache loading in a cluster
to one node at a time.
Fixes #2707

src/data/LedgerCache.cpp

@@ -224,6 +224,7 @@ LedgerCache::setFull()
         return;
 
     full_ = true;
+    isCurrentlyLoading_ = false;
     std::scoped_lock const lck{mtx_};
     deletes_.clear();
 }
@@ -290,4 +291,16 @@ LedgerCache::loadFromFile(std::string const& path, uint32_t minLatestSequence)
     return {};
 }
 
+void
+LedgerCache::startLoading()
+{
+    isCurrentlyLoading_ = true;
+}
+
+bool
+LedgerCache::isCurrentlyLoading() const
+{
+    return isCurrentlyLoading_;
+}
+
 }  // namespace data