CI Pipeline which builds & tests the container

To make sure our Hugging Face DLC are well tested, we need to create "integration" tests that run different kinds of training using the container. Those tests should be run automatically or on-demand. We can use Github Actions as CI for running the tests and `python` + docker to implement the integration tests.

Until #3 is implemented, we can use existing Containers from, e.g. `transformers` to run the tests. For "tests" script, i think we can use existing "examples/" from `transformers` or `peft` `trl`. We could structure the `tests/` folder maybe into:
* `local/` (run on a local machine GPU),
* `vertex` (run on Vertex)
* `gke` (run on GKE)

Example for a test:
0. build a container
1. starts a container on a GPU
2. runs a training using the container (few steps)
3. validates results
4. stops the container
-> repeat 1-4. with other tests.

In addition to "local" tests running on GPU instances, we should also run validation tests for GKE and Vertex AI.

* [ ] We need to implement strong CI tests, which run several tests, including training smaller models like BERT and bigger models Like Llama.
* [ ] We should test and validate PEFT
* [ ] Distributed Training
* [ ] Flash attention support
* [ ] Tests directly running on Vertex AI or GKE using vertex SDK