Add attn sink

[LJ-underdog]

Proposed changes

Please describe the motivation behind the pull request, whether it enables a new feature or fixes a bug. If there are associated pull requests or issues, please link them to the pull request.

Checklist

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• [x] I have added tests relevant to the introduced functionality, and the unit tests are passing locally
• [x] I have added the test to REGRESSION_TESTS list defined at the top of CMakeLists.txt in tests/CMakeLists.txt, IF the test takes more than 30 seconds to run.
• [x] I have added inline documentation which enables the maintainers with understanding the motivation
• [x] I have removed the stale documentation which is no longer relevant after this pull request
• [x] (If this change is user-facing) I have added release notes which provide the end users with a brief summary of the improvement from this pull request
• [x] I have run clang-format on all changed files
• [x] Any dependent changes have been merged

Discussion

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[cgmillette]

@LJ-underdog @DDEle Can you create a PR in the AITER repo, reference it here and update the description? Once AITER PR is passing, then we can move this one ahead. Thanks!

[LJ-underdog]

@LJ-underdog @DDEle Can you create a PR in the AITER repo, reference it here and update the description? Once AITER PR is passing, then we can move this one ahead. Thanks!

There is a PR in the AITER repo, it is already being tested. https://github.com/ROCm/aiter/pull/1272