Issue 191: Align readthedocs with VRS and VA-Spec style of one concept per page

[brendanreardon]

Issue 191: Restructure documentation to mirror VRS' and VA-Spec's

In this Pull Request, we refactor the "Data Model" section of the documentation to have one concept per page, like VRS' and VA-Spec's does. The structure of the Data Model section is now...

Data Model/
    Recipes/
        CanonicalAllele.rst
        ....
    Constraints/
        CopyChangeConstraint.rst
        ...
    Imported/
    CategoricalVariant.rst
    Constraint.rst

A summary of changes include:

• Recipes are listed first within the Data Model section per refactoring the documentation to present the model as Recipes-first.
• Categorical Variant and Constraint are listed on the Data Model root.
• The Constraints/ folder contains all of the Constraint subclasses.
• Each Concept's page has sections for (i) the readthedocs reference, (ii) Definition and Information Model (the def/ file generated from the schema), (iii) Examples, and (iv) Implementation Guidance

Pull Request checklist:

• Does the title of this Pull Request reference the corresponding Issue?
• Is the branch validating against pre-commit hooks? Run pre-commit run --all-files from the root directory.
• Is the branch passing tests? Run pytest tests/ from the root directory.

If the schema or examples were contributed to:

• Neither the schema nor the examples were contributed to with this Pull Request

[brendanreardon]

@DanielPuthawala LMK whenever you get a chance to look at this. It's not time sensitive. In particular, I'm curious what you think of the experience of having "Categorical Variant" and "Constraint" base classes in the Data Model root.

[brendanreardon]

Here is a link to the readthedocs for this pull request: https://cat-vrs--195.org.readthedocs.build/en/195/concepts/index.html

[DanielPuthawala]

Just one hangup on the layout of the Data Model page, but other than that, I love this structure. Super easy to navigate! So once we resolve that I reckon it's ready to be shipped!

[DanielPuthawala]

Great work, looks good to me!