Serialize collections into dump output

[dwong2708]

Summary:
Add support for serializing collections (aggregators of components) into the learning package dump.

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Description

Collections are aggregators of components.
The requirement is to include all collections involved in a learning package as part of the dump.

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Rationale

• Ensures that the learning package fully represents not only individual components but also their organizational structure.
• Facilitates reproducibility of how content is grouped and delivered.
• Provides clarity and consistency when restoring or inspecting a package.

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Acceptance Criteria

• A collections/ folder is created in the dump.
• Each collection is represented as a TOML file within the folder.