[Button] Align props more closely with Craft conventions (entry, link field, etc)

[joshuapease]

https://craftcms.com/docs/5.x/reference/field-types/link.html#settings

• Add ariaLabel
• Change href to url (entries and link fields use url)
• Consider title
• Consider download
• Align target prop to expect _blank
• Adjust rel: rel: target == '_blank' ? 'noopener' : null,

Consider this syntax for attrs

{% tag el with {
   ...attrs,
    'aria-label': ariaLabel ??? attrs.ariaLabel ?? null,
} %}