feat: Resolve Dockerfile ARGs pulling base images

[HofmeisterAn]

What does this PR do?

This PR extracts ARG statements from the Dockerfile and replaces variables in FROM statements with their values to identify all included base images.

Why is it important?

When Testcontainers for .NET builds an image using ImageFromDockerfileBuilder, it needs to pre-pull the base images referenced in the Dockerfile. Previously, it didn't handle FROM statements with ARG variables, these were skipped. This PR fixes that by resolving ARG statements, using the Dockerfile's default values or any build arguments that override them.

Related issues

• Closes [Enhancement]: Resolve variables (ARGs) during Docker image build #980

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