Add machine translation disclaimer

[roadlittledawn]

Description

• Adds a machine translation callout/disclaimer to the top of any translated page that has translationType: machine in frontmatter. for now any page that uses docPage.js template, which i believe should cover relevant pages for now
• Adds type def for translationType in case no instances exist in frontmatter so Gatsby doesn't freak out when it sees it in graphql queries
• Adds long form disclaimer doc from other PR (linked in issue)
• Bumps theme to latest to be able to disable Link component's auto localizing link when linking to english version of localized page
• Adds feather globe icon

Related issues / PRs

Closes #2537

Screenshot(s)

[github-actions]

Hi @roadlittledawn 👋
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[gatsby-cloud]

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