feat(astro): Add support for custom menu items

[wobsoriano]

Description

This PR adds support for custom menu items in the <UserButton /> Astro component. It implements the same behavior with the React counterpart, with two exceptions:

1. The onClick prop for custom actions is not implemented, since Astro components are executed on the server and is serialized. Instead, we're using a CustomEvent with a clickIdentifier prop to identify which menu item has been clicked. Maybe we can remove clickIdentifier and just use the label as identifier?
2. The labelIcon prop is now a slot.

React components to follow.

Closes ECO-130

Usage:

<UserButton><UserButton.MenuItems><UserButton.Linklabel="Profile" href="/profile"><SomeIconslot="label-icon" /></UserButton.Link><UserButton.Actionlabel="Terms" open="terms"><TermsIconslot="label-icon" /></UserButton.Action><UserButton.Actionlabel="Open chat" clickIdentifier="open_chat"><ChatIconslot="label-icon" /></UserButton.Action></UserButton.MenuItems><UserButton.UserProfilePagelabel="Terms" url="terms"><TermsIconslot="label-icon" /><div><h1>Custom Terms Page</h1><p>This is the custom terms page</p></div></UserButton.UserProfilePage></UserButton><script>document.addEventListener('clerk:menu-item-click',(e)=>{if(e.detail==='open_chat'){/* do something */}},false,);</script>

Closes ECO-130

Checklist

• npm test runs as expected.
• npm run build runs as expected.
• (If applicable) JSDoc comments have been added or updated for any package exports
• (If applicable) Documentation has been updated

Type of change

• 🐛 Bug fix
• 🌟 New feature
• 🔨 Breaking change
• 📖 Refactoring / dependency upgrade / documentation
• other:

[changeset-bot]

🦋 Changeset detected

Latest commit: 7542e82

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

This PR includes changesets to release 1 package

Name	Type
@clerk/astro	Minor

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