Enable SQLite shared cache mode.

This allows all threads accessing the same database to share sqlite
objects. This, for example, fixes the issue with several threads
simultaneously writing to the same database file.

See https://www.sqlite.org/sharedcache.html

Addresses BIT-1325

src/logging/writers/sqlite/SQLite.cc

@@ -120,6 +120,9 @@ bool SQLite::DoInit(const WriterInfo& info, int arg_num_fields,
 		return false;
 		}
 
+	// Allow connections to same DB to use single data/schema cache. Also allows simultaneous writes to one file.
+	sqlite3_enable_shared_cache(1);
+
 	num_fields = arg_num_fields;
 	fields = arg_fields;