Redefines the approach to building and managing Docker images within testcontainers by introducing the DockerImage class. This class encapsulates the logic for building images from Dockerfiles and pulling images from repositories.

Key Changes:
- Implements DockerImage as a central class for image operations, including build, pull, get, and remove.
- Add this class as acceptable image param type for DockerContainer and DockerClient
- Enables direct Dockerfile support while preserving the option to pull existing images, facilitating a more dynamic testing setup.

This refactor addresses feedback on the initial implementation, proposing a cleaner, more extensible design.