chore: Reduce size of docker image

[titom73]

Description

• Update base image from -slim to -alpine
• Implement an intermediate builder to reduce size of docker image
• Implement a .dockerignore file to not copy non-necessary content

ghcr.io/arista-netdevops-community/anta   dev-py-alpine   174234061901   22 seconds ago   97.9MB
ghcr.io/arista-netdevops-community/anta   dev             690d2d1cf3de   19 hours ago     223MB
ghcr.io/arista-netdevops-community/anta   latest          a8e3954c544b   4 weeks ago      197MB

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my code
• I have run pre-commit for code linting and typing (pre-commit run)
• I have made corresponding changes to the documentation: N/A
• I have added tests that prove my fix is effective or that my feature works: N/A
• New and existing unit tests pass locally with my changes (tox -e testenv)

[mtache]

🐳