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.Link label="Profile" href="/profile">
            <SomeIcon slot="label-icon" />
        </UserButton.Link>
        <UserButton.Action label="Terms" open="terms">
            <TermsIcon slot="label-icon" />
        </UserButton.Action>
        <UserButton.Action label="Open chat" clickIdentifier="open_chat">
            <ChatIcon slot="label-icon" />
        </UserButton.Action>
    </UserButton.MenuItems>
    <UserButton.UserProfilePage label="Terms" url="terms">
        <TermsIcon slot="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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