feat: add CLI option for schema-only generation

[sserrata]

Description

Alternative implementation to #1203. Adds CLI option for generating only schemas to the specified output directory.

Motivation and Context

In support of use cases where users only need/want the schemas to be generated without having to modify the plugin config for the given API.

How Has This Been Tested?

TBD

Types of changes

• New feature (non-breaking change which adds functionality)

[github-actions]

Visit the preview URL for this PR (updated for commit 3b976e7):

https://docusaurus-openapi-36b86--pr1228-w0mzayhy.web.app

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[sserrata]

Test results:

Generate schemas for single version

docusaurus gen-api-docs petstore --schemas-only

Successfully created "docs/petstore/schemas"
Successfully created "docs/petstore/apiresponse.schema.mdx"
Successfully created "docs/petstore/cat.schema.mdx"
Successfully created "docs/petstore/category.schema.mdx"
Successfully created "docs/petstore/dog.schema.mdx"
Successfully created "docs/petstore/honeybee.schema.mdx"
Successfully created "docs/petstore/id.schema.mdx"
Successfully created "docs/petstore/order.schema.mdx"
Successfully created "docs/petstore/pet.schema.mdx"
Successfully created "docs/petstore/tag.schema.mdx"
Successfully created "docs/petstore/user.schema.mdx"
✨  Done in 1.74s.

Generate schemas for multiple versions

docusaurus gen-api-docs petstore_versioned --schemas-only --all-versions

Successfully created "docs/petstore_versioned/schemas"
Successfully created "docs/petstore_versioned/apiresponse.schema.mdx"
Successfully created "docs/petstore_versioned/cat.schema.mdx"
Successfully created "docs/petstore_versioned/category.schema.mdx"
Successfully created "docs/petstore_versioned/dog.schema.mdx"
Successfully created "docs/petstore_versioned/honeybee.schema.mdx"
Successfully created "docs/petstore_versioned/id.schema.mdx"
Successfully created "docs/petstore_versioned/order.schema.mdx"
Successfully created "docs/petstore_versioned/pet.schema.mdx"
Successfully created "docs/petstore_versioned/tag.schema.mdx"
Successfully created "docs/petstore_versioned/user.schema.mdx"
Successfully created "docs/petstore_versioned/versions.json"
Successfully created "docs/petstore_versioned/1.0.0/schemas"
Successfully created "docs/petstore_versioned/1.0.0/apiresponse.schema.mdx"
Successfully created "docs/petstore_versioned/1.0.0/cat.schema.mdx"
Successfully created "docs/petstore_versioned/1.0.0/category.schema.mdx"
Successfully created "docs/petstore_versioned/1.0.0/dog.schema.mdx"
Successfully created "docs/petstore_versioned/1.0.0/bee.schema.mdx"
Successfully created "docs/petstore_versioned/1.0.0/id.schema.mdx"
Successfully created "docs/petstore_versioned/1.0.0/order.schema.mdx"
Successfully created "docs/petstore_versioned/1.0.0/pet.schema.mdx"
Successfully created "docs/petstore_versioned/1.0.0/tag.schema.mdx"
Successfully created "docs/petstore_versioned/1.0.0/user.schema.mdx"
✨  Done in 2.31s.