Reference RuleWithActions & Transaction object instead of copying values in RuleMessage

- Because the lifetime of the RuleMessage instances do not extend beyond
  the lifetime of the enclosing RuleWithActions & Transaction,
  RuleMessage can just reference it and simplify its definition.
- Additionally, make the references const to show that it doesn't modify it.
- Replace RuleMessage copy constructor with default implementations.
- Removed unused RuleMessage assignment operator (which cannot be implemented
  now that it has reference members).
- Removed constructor from RuleMessage pointer.
- Addressed Sonarcloud suggestions: Do not use the constructor's
  initializer list for data member "xxx". Use the in-class initializer
  instead.

src/audit_log/writer/parallel.cc

@@ -123,7 +123,7 @@ bool Parallel::write(Transaction *transaction, int parts, std::string *error) {
     }
 
     const auto &logPath = m_audit->m_storage_dir;
-    fileName = logPath + fileName + "-" + *transaction->m_id.get();
+    fileName = logPath + fileName + "-" + transaction->m_id;
 
     if (logPath.empty()) {
         error->assign("Log path is not valid.");