Add Dockerfile for GPU

[alesolano]

Description

Now that we have a Dockerfile.cpu, we need a Dockerfile.gpu. This should be tested in a machine with a GPU.
Also, as we will have two Dockerfiles and two requirements files, we should check what the best practices are for managing this duplicity.

Requirements

Things you need in order to complete the issue.

• Machine with a GPU
• Knowledge about best practices for managing two Dockerfiles.

Acceptance Criteria

Criteria that must be met in order to close the issue successfully.

• A Dockerfile for gpu is created.
• This new Dockerfile can be built successfully. Check command: python -c "import tensorflow as tf; print(tf.reduce_sum(tf.random.normal([1000, 1000])))"
• The two Dockerfiles are managed in the best way.