Added blog post "FlexAttention: The Flexibility of PyTorch with the Performance of FlashAttention" (#1701)

* Added blog post "FlexAttention: The Flexibility of PyTorch with the Performance of FlashAttention"

Signed-off-by: Chris Abraham <[email protected]>

* Update publish date

Signed-off-by: Chris Abraham <[email protected]>

* Update 2024-08-07-flexattention.md

* Update 2024-08-07-flexattention.md

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Signed-off-by: Chris Abraham <[email protected]>
Co-authored-by: Kylie Wagar-Dirks <[email protected]>

Author: cjyabraham