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/RPCOverload_test.cpp

@@ -45,7 +45,9 @@ public:
                 jv = jv[jss::result];
             // When booted, we just get a null json response
             if (jv.isNull())
+            {
                 booted = true;
+            }
             else if (!(jv.isMember(jss::status) && (jv[jss::status] == "success")))
             {
                 // Don't use BEAST_EXPECT above b/c it will be called a