Add test scripts for llama2-7b int8/bf16 models

[xy12181]

Tested:

$ ./MaxText/tests/inference/test_llama2_7b_int8.sh
$ ./MaxText/tests/inference/test_llama2_7b_bf16.sh

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[xy12181]

@vipannalla PTAL. Thanks!

[wyzhang]

nit: for future reference, I find it useful to

args=(
...
)
python "${args[@]}"

which allow us to add comment explain what an argument does.

Fine to keep as is

[xy12181]

Updated. Thanks!

[xy12181]

@vipannalla et al. could you please help review? thanks!