Update inserting tables in `fields.markdoc`/`fields.mdx` to include a table header row by default and remove button to toggle table header in `fields.mdx`

[emmatown]

Fixes #1283

[changeset-bot[bot]]

🦋 Changeset detected

Latest commit: 1a0acfebf965b0cada52adc55e1481b0e812dccb

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 13 packages

| Name | Type | | --------------------------- | ----- | | @keystatic/core | Patch | | @keystar/docs | Patch | | @example/astro-content | Patch | | @example/astro | Patch | | @example/localization | Patch | | @example/next-app | Patch | | @example/next-block-builder | Patch | | @example/next-pages | Patch | | @keystatic/remix-test-app | Patch | | keystatic-docs | Patch | | @keystatic/templates-astro | Patch | | @keystatic/templates-nextjs | Patch | | @keystatic/templates-remix | Patch |

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