Starcoder2 model - bis (#29215)

* Copy model

* changes

* misc

* fixes

* add embed and residual dropout (#30)

* misc

* remove rms norm and gated MLP

* remove copied mentions where its not a copy anymore

* remove unused _shape

* copied from mistral instead

* fix copies

* fix copies

* add not doctested

* fix

* fix copyright

* Update docs/source/en/model_doc/starcoder2.md

Co-authored-by: Arthur <48595927+ArthurZucker@users.noreply.github.com>

* Update src/transformers/models/starcoder2/configuration_starcoder2.py

Co-authored-by: Arthur <48595927+ArthurZucker@users.noreply.github.com>

* Update src/transformers/models/starcoder2/configuration_starcoder2.py

Co-authored-by: Arthur <48595927+ArthurZucker@users.noreply.github.com>

* fix doc

* revert some changes

* add fa2 tests

* fix styling nit

* fix

* push dummy docs

---------

Co-authored-by: Joel Lamy-Poirier <joel.lamy-poirier@servicenow.com>
Co-authored-by: younesbelkada <younesbelkada@gmail.com>
Co-authored-by: Younes Belkada <49240599+younesbelkada@users.noreply.github.com>
Co-authored-by: Arthur <48595927+ArthurZucker@users.noreply.github.com>