[Databuckets] Nested Databuckets Protections and Improvements (#4748)

* Check for valid JSON before using it

* Do not allow nested keys to set be set an expiration

* Prevent overwriting of existing object or array

* Nested deletion support

* Update data_bucket.cpp

* Test cases

* More test cases, fix

* Update databuckets.cpp

* Update databuckets.cpp

* Basic databucket tests

* Update databuckets.cpp

* Update databuckets.cpp

common/strings.h

@@ -45,6 +45,7 @@
 #include <type_traits>
 
 #include <fmt/format.h>
+#include <cereal/external/rapidjson/document.h>
 
 #ifndef _WIN32
 // this doesn't appear to affect linux-based systems..need feedback for _WIN64
@@ -188,6 +189,7 @@ public:
 	}
 
 	static std::string Slugify(const std::string &input, const std::string &separator = "-");
+	static bool IsValidJson(const std::string& json);
 };
 
 const std::string StringFormat(const char *format, ...);