Engine V7: JSONPath support

[khvn26]

To simplify later Evaluation Context extensions, we need to add JSONPath capabilities to the Flagsmith Engine.

1. Select a correct, lightweight, performant JSONPath library to use. Extension support is welcome, but we should be conscious of other engine implementations, and JSONPath implementations in their respective languages, when assessing a list of extensions to support.
2. Reimplement the get_context_value function using JSONPath.

[khvn26]

Most of the target languages for local evaluation have RFC 9535 compliant libraries, with exceptions of Elixir and Java:

Language	Library	RFC 9535 compliant
C#	https://github.com/json-everything/json-everything	✅
Elixir	https://github.com/secomind/exjsonpath	❌
Go	https://github.com/theory/jsonpath	✅
Java	https://github.com/json-path/JsonPath	❌
JS	https://github.com/jg-rp/json-p3	✅
PHP	https://github.com/loilo/jsonpath-php	✅
Python	https://github.com/jg-rp/python-jsonpath-rfc9535	✅
Ruby	https://github.com/jg-rp/ruby-json-p3	✅
Rust	https://github.com/besok/jsonpath-rust	✅

GH issues to watch for remaining RFC implementations:

• Consider implementing RFC 9535 json-path/JsonPath#999
• Consider implementing RFC 9535 secomind/exjsonpath#33

#243 opened with a reference implementation.