[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.cpp

@@ -936,3 +936,11 @@ std::string Strings::Slugify(const std::string& input, const std::string& separa
 
 	return slug;
 }
+
+bool Strings::IsValidJson(const std::string &json)
+{
+	rapidjson::Document    doc;
+	rapidjson::ParseResult result = doc.Parse(json.c_str());
+
+	return result;
+}