feat(models): adds subtypes to most entities in the model

[shirshanka]

Subtypes are useful. Most entities should have them.
This PR adds subtypes to most of the entities in the metadata model.

This PR does NOT add support for GQL mapping or rendering these subtypes in the UI.
That will be covered by a subsequent PR.

Checklist

• The PR conforms to DataHub's Contributing Guideline (particularly Commit Message Format)
• Links to related issues (if applicable)
• Tests for the changes have been added/updated (if applicable)
• Docs related to the changes have been added/updated (if applicable). If a new feature has been added a Usage Guide has been added for the same.
• For any breaking change/potential downtime/deprecation/big changes an entry has been made in Updating DataHub

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

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[ryota-cloud]

thanks!