Fix Dropout Implementation in Graphormer
Author: alexanderkrauck
Pull request: yes

# What does this PR do?

This commit corrects the dropout implementation in Graphormer, aligning it with the original implementation (https://github.com/microsoft/Graphormer) and improving performance. Specifically:

1. The `attention_dropout` variable, intended for use in GraphormerMultiheadAttention, was defined but not used. This has been corrected to use `attention_dropout` instead of the regular `dropout`.
2. The `activation_dropout` for the activations in the feed-forward layers was missing. Instead, the regular `dropout` was used. This commit adds `activation_dropout` to the feed-forward layers and to the GraphormerConfig including documentation.

These changes ensure the dropout implementation matches the original Graphormer and delivers empirically better performance.



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@clefourrier 

Comments:
Hi @clefourrier and others,
this is the first time contributing to Huggingface for me. In the course of my thesis I found some improvements/fixes to your current Graphormer implementation including this one which is quite simple but has a big impact and should be easy to review. I plan to make some more pull requests with more performance related changes to speed Graphormer up and possibly also to add the 3D version in the following days/weeks. Feel free to reach out.
Best wishes, Alexander

This issue has been automatically marked as stale because it has not had recent activity. If you think this still needs to be addressed please comment on this thread.

Please note that issues that do not follow the [contributing guidelines](https://github.com/huggingface/transformers/blob/main/CONTRIBUTING.md) are likely to be ignored.

It still needs to be adressed! @clefourrier or whoever is responsible for it, am I doing something wrong with my pull request or what is taking so long for anyone to anwer?! How am I supposed to contribute if I am being ignored. 

Hi @alexanderkrauck !
I have been very busy taking care of the Open LLM Leaderboard, and I put the graph transformers issues on the backburner for the summer. I was hoping to come back to this quite earlier than now, I'm very sorry about that.
I'll do my best to come back to these before the end of September

@amyeroberts or @ArthurZucker ?