fix: support root-relative URLs in EsButton

[ericdouglaspratt]

🔗 Linked issue

• https://energysage.atlassian.net/browse/CED-1900

❓ Type of change

• 📖 Documentation (updates to the documentation or readme)
• 🐞 Bug fix (a non-breaking change that fixes an issue)
• 👌 Enhancement (improving an existing functionality like performance)
• ✨ New feature (a non-breaking change that adds functionality)
• ⚠️ Breaking change (fix or feature that would cause existing functionality to change)

📚 Description

• Previously, EsButton, when given either an href or to prop, would pass those to NuxtLink. NuxtLink will externally navigate with a full URL like https://www.google.com, but if provided a root-relative URL like /market/start/, it will attempt to internally navigate and result in a 404, even though that URL does exist on our domain.
• This changes EsButton so that if href is provided, we use an <a> tag, and if to is provided, we use a NuxtLink. This allows downstream applications to decide whether they need an internal or external navigation on a link, rather than the design system forcing one upon them that may not work.

🥼 Testing

• Tested locally with es-cms-pages and LandingCtaFullWidthImage

🧐 Feedback Requested / Focus Areas

• I have linked an issue or discussion.
• I have updated the documentation accordingly.
• I have documented testing approach

[swarmia]

✅  Linked to Task CED-1900 · Upgrade homepage to Nuxt 3 in es-cms-pages
➡️  Part of Epic CED-1443 · Upgrade CMS micro frontends to Nuxt 3 [LC]

[hroth1994]

LGTM! 🌟