chore: config Dockerfile.benchmark in gitattributes

[o-az]

Summary

currently the file doesn't have syntax highlighting in github. Marking it in .gitattributes manually tells github to add Dockerfile syntax highlighting to it

Test Plan

[dyc3]

Not a blocker for this PR, but typically I name give files the extension .dockerfile to avoid this problem. I would also accept renaming this file (and updating the name across the codebase).

[o-az]

ld also accept renaming this file (and updating the name across the codebase).

I recall somewhere in docker's docs it showing that the convention is Dockerfile.*

[o-az]

ld also accept renaming this file (and updating the name across the codebase).

I recall somewhere in docker's docs it showing that the convention is Dockerfile.*

Actually I'm wrong. Looks like it's *.Dockerfile https://docs.docker.com/build/building/packaging/#filename