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/jtx/impl/vault.cpp

@@ -12,7 +12,7 @@ namespace test {
 namespace jtx {
 
 std::tuple<Json::Value, Keylet>
-Vault::create(CreateArgs const& args)
+Vault::create(CreateArgs const& args) const
 {
     auto keylet = keylet::vault(args.owner.id(), env.seq(args.owner));
     Json::Value jv;