refactor: Add simple clang-tidy readability checks (#6556)

This change enables the following clang-tidy checks:
-  readability-avoid-nested-conditional-operator,
-  readability-avoid-return-with-void-value,
-  readability-braces-around-statements,
-  readability-const-return-type,
-  readability-container-contains,
-  readability-container-size-empty,
-  readability-else-after-return,
-  readability-make-member-function-const,
-  readability-redundant-casting,
-  readability-redundant-inline-specifier,
-  readability-redundant-member-init,
-  readability-redundant-string-init,
-  readability-reference-to-constructed-temporary,
-  readability-static-definition

src/test/rpc/Version_test.cpp

@@ -42,10 +42,12 @@ class Version_test : public beast::unit_test::suite
 
         auto badVersion = [](Json::Value const& re) -> bool {
             if (re.isMember("error_what"))
+            {
                 if (re["error_what"].isString())
                 {
                     return re["error_what"].asString().find(jss::invalid_API_version.c_str()) == 0;
                 }
+            }
             return false;
         };