feat: Graceful shutdown with old web server (#2786)

- Stop accepting connections during graceful shutdown in the old web server
- Stop all the services before Clio exits
- Move cache saving into stop callback

src/data/LedgerCache.cpp

@@ -265,7 +265,7 @@ LedgerCache::saveToFile(std::string const& path) const
     }
 
     impl::LedgerCacheFile file{path};
-    std::unique_lock const lock{mtx_};
+    std::shared_lock const lock{mtx_};
     impl::LedgerCacheFile::DataView const data{.latestSeq = latestSeq_, .map = map_, .deleted = deleted_};
     return file.write(data);
 }