[2.x] Add a tag dropdown link

[dillingham]

PR adds <a> tag to the <jet-dropdown-link> component.

When adding spark billing, it would be cleaner to:

<jet-dropdown-link as="a" :href="route('spark.portal')">
    Billing
</jet-dropdown-link>

compared to manually adding the tailwind classes to <a> to avoid inertia navigation.

<a :href="route('spark.portal')" class="block px-4 py-2 text-sm leading-5 text-gray-700 hover:bg-gray-100 focus:outline-none focus:bg-gray-100 transition duration-150 ease-in-out">
    Billing
</a>

Used as="a" to stay in line with as="button"

[driesvints]

as="link" might be more descriptive?

[taylorotwell]

@driesvints it's an inertia-link by default so as=link might sound like inertia link.