[Model] Add support for Qwen2 for embeddings

[DarkLight1337]

A newer version of #5611 and #6282 since the source repo has been archived.

FIX #5600
FIX #5827
FIX #6015

[github-actions]

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[mgoin]

How are these models different? It would be good to avoid using another ~7B model in this test

[DarkLight1337]

One uses Qwen2Model, while the other uses Qwen2ForCausalLM architecture.

[mgoin]

Will this be able to be controlled by the pooling args we spoke about offline?

[DarkLight1337]

Yes - these are the model's default values which can be overridden.

[DarkLight1337]

I still need to update the tests since these models don't have sentence-transformers equivalents.

Nevermind, I was misled by the warning message. It's intended that ssmits/Qwen2-7B-Instruct-embed-base uses mean pooling instead of last pooling.

[DarkLight1337]

I have fixed the tests.

[mergify]

This pull request has merge conflicts that must be resolved before it can be
merged. Please rebase the PR, @DarkLight1337.

https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/working-with-forks/syncing-a-fork