[Enhancement] Add Open Parameters to Flat_object Field Type

Is your feature request related to a problem? Please describe. Flat objects currently do not support open parameters. Looking forward to add open parameter to increase better search results.

Describe the solution you'd like The following open parameters setting are useful to consider to add in, including normalizer, docValues, ignoreAbove, nullValue, similarity, and depthlimit.

normalizer: allow lowercase, uppercase docValues: allow to set docValues to be false ignoreAbove: allow to set if the length of a field is go above certain limit then ignore the document. nullValue: allow to set nullValue to others similarity: allow to set similarity setting depthlimit: allow to set maximum depth limitation to the JSON document

Additional context Add any other context or screenshots about the feature request here.