Express DANDI data models in LinkML

[candleindark]

The goal of this PR is to provide representations of DANDI data models in LinkML.

The initial representations in LinkML are generated with https://github.com/candleindark/linkml-aind-model a fork of https://github.com/DailyDreaming/linkml-aind-model.

Incremental targets:

• [ ] Develop the tool at https://github.com/candleindark/linkml-aind-model to produce more correct and complete conversion from Pydantic models to a LinkML schema
• [ ] Set up a CI project to check various existing data instances against the produced LinkML schema
• [ ] Use the produced LinkML schema to produce Pydantic models to replace the existing Pydantic models in the dandi-schema project and check how well the existing tests in the project pass.
• [ ] Repeat the above steps to obtain a more complete and accurate LinkML schema if needed

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 91.81%. Comparing base (dc15401) to head (55992f0).

Additional details and impacted files

```diff @@ Coverage Diff @@ ## to-linkml #240 +/- ## ============================================= + Coverage 87.39% 91.81% +4.41% ============================================= Files 16 16 Lines 1722 1722 ============================================= + Hits 1505 1581 +76 + Misses 217 141 -76 ``` | [Flag](https://app.codecov.io/gh/dandi/dandi-schema/pull/240/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=dandi) | Coverage Δ | | |---|---|---| | [unittests](https://app.codecov.io/gh/dandi/dandi-schema/pull/240/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=dandi) | `91.81% <ø> (+4.41%)` | :arrow_up: | Flags with carried forward coverage won't be shown. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=dandi#carryforward-flags-in-the-pull-request-comment) to find out more.

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