add new feature flag to intern value string

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Feature request

Existing scenario

I think the INTERN_FIELD_NAMES flag is great thing to have, which is turned on by default. This would save greatly on the memory footprint especially when the message size is huge, imagine ~3.2 million position messages, all with same key like 'portfolio', 'book'.
Instead of having ~3.2 million of portfolio in parsing each batch of message in heap, with INTERN_FIELD_NAMES, it would result in only one portfolio on the string pool regardless of the message sizes, being ~3.2 million or even more.

Changes proposed

A similar feature flag could be provided, even turned on by default as well, when parsing the values.
So that, back to the ~3.2 million records example, instead of having ~3.2 million portfolio names in the heap, the similar feature flag would result in only around ~200 portfolio name (like Jason, Jackson) in the string pool.

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