Fix hf_quant_config with kv cache type

[jenchen13]

What does this PR do?

Type of change: ? Bug fix

Fix hf_quant_config with correct kv cache type for FP8

Overview: ?

Usage

# Add a code snippet demonstrating how to use this

Testing

will test export with KV cache fp8 enabled

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 74.37%. Comparing base (a113bea) to head (247bc54).
⚠️ Report is 3 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #557   +/-   ##
=======================================
  Coverage   74.37%   74.37%           
=======================================
  Files         182      182           
  Lines       18219    18219           
=======================================
  Hits        13550    13550           
  Misses       4669     4669           

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[meenchen]

Could you also add FP4 KV support? TRT-LLM actually supports FP4 kv now.

[jenchen13]

just added