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/request_body_processor/multipart.cc

@@ -74,7 +74,7 @@ void MultipartPartTmpFile::Open() {
     strftime(tstr, std::size(tstr), "/%Y%m%d-%H%M%S", &timeinfo);
 
     std::string path = m_transaction->m_rules->m_uploadDirectory.m_value;
-    path = path + tstr + "-" + *m_transaction->m_id.get();
+    path = path + tstr + "-" + m_transaction->m_id;
     path += "-file-XXXXXX";
 
 #ifndef WIN32