Create and publish markdown templates for all asset documentation pages

[mattrosno]

Once asset documentation has been added to the schema (#792) and once that index content is wired up to conditionally render asset page tabs for usage, style, code, and accessibility (#793), we'll want markdown templates for each of those sub-pages so contributors can copy/paste the template so they have a skeleton of recommended headings and sections to fill out.

We have two component usage docs templates:

• https://carbondesignsystem.com/contributing/component/#template-for-components-with-one-variant
• https://carbondesignsystem.com/contributing/component/#template-for-components-with-multiple-variants

No style templates:

• https://carbondesignsystem.com/contributing/component/#style-guidance

One code template:

• https://carbondesignsystem.com/contributing/component/#code-guidance

No accessibility template.

And two pattern templates:

• https://carbondesignsystem.com/contributing/pattern/#how-to-write-a-pattern

Acceptance criteria

• [ ] The platform web app has contribution guidance where you can understand the indent of each asset documentation page, as well as templates to copy so we can guide users to have consistent asset documentation

[mattrosno]

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