ci:build and test workflow to backend API

[andresvicentehector]

###Change

    Added a new GitHub Actions workflow for the MyLibrary Backend project.
    This CI/CD pipeline includes:
    
    -     Installing dependencies and running tests.
    -     Building a Docker image from the Dockerfile.
    -     Exporting the image as an artifact.
    -     Publishing the image to DockerHub based on the trigger event (release, push, workflow_dispatch).
    -     Optionally updating the DockerHub repository description using docker-description.md.

###How to Test

        Push to any branch and verify that the build-and-test and docker workflows run.
        Create a release or trigger the workflow manually via workflow_dispatch and check that:
        The image is pushed to DockerHub.
         The repository description is updated (if selected).
        Monitor the Actions tab in GitHub to ensure each job runs successfully.
        Check that the image is available on DockerHub under aiod/mylibrary-backend.

###Checklist

- [ ] Tests are run as part of the CI (pytest).
- [ ] Documentation is included directly in the workflow file.
- [ ] Self-review completed:
- [ ]  No unintended changes were committed.
- [ ]  Each job was validated independently.
- [ ] Comments were added in the YAML where things may not be intuitive.
- [ ] All CI checks pass.

###Related Issues
Closes #30