… possible, and as pybind11::object otherwise (nv-morpheus#455)

* Add an optional `unserializable_handler_fn` callback to `mrc::pymrc::cast_from_pyobject` which will be invoked for any unsupported Python object. Allowing for serializing unsupported object.
ex:
```cpp
    pymrc::unserializable_handler_fn_t handler_fn = [](const py::object& source,
                                                       const std::string& path) {
        return nlohmann::json(py::cast<float>(source));
    };

    // decimal.Decimal is not serializable
    py::object Decimal = py::module_::import("decimal").attr("Decimal");
    py::object o       = Decimal("1.0");
    EXPECT_EQ(pymrc::cast_from_pyobject(o, handler_fn), nlohmann::json(1.0));
```

* Add `JSONValues` container class which is an immutable container for holding Python values as `nlohmann::json` objects if possible, and as `pybind11::object` otherwise. The container can be copied and moved, but the underlying `nlohmann::json` object is immutable.
* Updates `nlohmann_json` from 3.9 to 3.11 for `patch_inplace` method.
* Incorporates ideas from @drobison00's PR nv-morpheus#417 with three key differences:

  1. Changes to the `cast_from_pyobject` are opt-in when `unserializable_handler_fn` is provided, otherwise there is no behavior change to the method.
  2. Unserializable objects are stored in `JSONValues` rather than a global cache.
  3. Does not rely on parsing the place-holder values.

This PR is related to nv-morpheus/Morpheus#1560

Authors:
  - David Gardner (https://github.com/dagardner-nv)
  - Devin Robison (https://github.com/drobison00)

Approvers:
  - Michael Demoret (https://github.com/mdemoret-nv)

URL: nv-morpheus#455