Update modeling_blenderbot.py
Made the `BlenderbotEncoderLayer` have similar optional arguments to the `BlenderbotDecoderLayer` and other classes.

Fixes the `forward` call of the `BlenderbotEncoderLayer`.

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Models:

- albert, bert, xlm: @LysandreJik
- blenderbot, bart, marian, pegasus, encoderdecoder,  t5: @patrickvonplaten, @patil-suraj
- longformer, reformer, transfoxl, xlnet: @patrickvonplaten
- fsmt: @stas00
- funnel: @sgugger
- gpt2: @patrickvonplaten, @LysandreJik
- rag: @patrickvonplaten, @lhoestq
- tensorflow: @LysandreJik

Library:

- benchmarks: @patrickvonplaten
- deepspeed: @stas00
- ray/raytune: @richardliaw, @amogkam
- text generation: @patrickvonplaten
- tokenizers: @n1t0, @LysandreJik
- trainer: @sgugger
- pipelines: @LysandreJik

Documentation: @sgugger

HF projects:

- datasets: [different repo](https://github.com/huggingface/datasets)
- rust tokenizers: [different repo](https://github.com/huggingface/tokenizers)

Examples:

- maintained examples (not research project or legacy): @sgugger, @patil-suraj
- research_projects/bert-loses-patience: @JetRunner
- research_projects/distillation: @VictorSanh

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The docs for this PR live [here](https://moon-ci-docs.huggingface.co/docs/transformers/pr_15382). All of your documentation changes will be reflected on that endpoint.<|||||>Could you also update this in `modeling_mbart.py` as well, because the encoder and decoder modules are in blenderbot are copied from mbart so we need to fix both of those. So

- update the mbart file
- and run `make fix-copies`, which will then fix this for all other models which have a similar copy.

Let me know if you need help with it :) <|||||>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/master/CONTRIBUTING.md) are likely to be ignored.