This pull request adds support for associating external links with experiments in the database and view models, and refactors related Pydantic models for better code reuse. The main changes are the addition of an external_links property to experiments, the introduction of a reusable ExternalLink model, and the relocation of the OfficialCollection model for consistency.

Database and Model Changes:

• Added a new external_links column of type JSONB (not nullable) to the experiments table via Alembic migration.
• Updated the Experiment SQLAlchemy model to include the new external_links column with a default empty dictionary.

Pydantic Model Refactoring:

• Introduced a reusable ExternalLink Pydantic model in components/external_link.py and updated references in experiment and score set view models to use this shared model. [1] [2] [3] [4]
• Moved the OfficialCollection model to collection.py for consistency, and updated imports throughout the codebase. [1] [2] [3] [4]

Code Cleanup:

• Removed duplicate definitions of ExternalLink and OfficialCollection from score_set.py and experiment.py, ensuring these models are only defined once and imported where needed. [1] [2]
• Minor import ordering and typing improvements in affected files. [1] [2]