Remove enforced left-alignment for table headers

[dstaley]

🎟️ Asana Task
🔍 Preview Link

---

Description

This removes the default text-align: left; rule for table headers, allowing authors to align their headers whichever way sparks joy. By default, table headers will now be center aligned.

PR Checklist 🚀

Items in this checklist may not may not apply to your PR, but please consider each item carefully.

• Add Asana and Preview links above.
• Conduct thorough self-review.
• Add or update tests as appropriate.
• Conduct reasonable cross browser testing for both compatibility and responsive behavior (We have a Sauce Labs account for this, if you don't have access, just ask!).
• Conduct reasonable accessibility review (use the WAS as a guide or an axe browser plugin until we establish more formal checks).
• Identify (in the description above) and document (add Asana tasks on this board) any technical debt that you're aware of, but are not addressing as part of this PR.

[vercel]

This pull request is being automatically deployed with Vercel (learn more).
To see the status of your deployment, click below or on the icon next to each commit.

🔍 Inspect: https://vercel.com/hashicorp/react-components/Bi6Jbnp29mrqYbM5eB6XsvgzC6cH
✅ Preview: https://react-components-git-dsth-no-left-align-hashicorp.vercel.app

[changeset-bot]

🦋 Changeset detected

Latest commit: d58c090

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

This PR includes changesets to release 1 package

Name	Type
@hashicorp/react-content	Minor

Not sure what this means? Click here to learn what changesets are.

Click here if you're a maintainer who wants to add another changeset to this PR