feat: Port CvButtonSkeleton to Vue3

[OlkaB]

Contributes to #1469

## What did you do?
Port CvButtonSkeleton to Vue3

## Why did you do it?
Hope this will help to finish transition before Vue2 EOL

How have you tested it?

please see CvButtonSkeleton.spec.js + CvButtonSkeleton.stories.js
compared behaviours with Vue2 storybook

Were docs updated if needed?

• Yes

[davidnixon]

Wow! Thanks for helping out here! Almost perfect. the only thing I see is that CvButtonSkeleton is imported in index.js but not exported. So for me I see nothing in the story and I see this in the console log:

[Vue warn]: Failed to resolve component: cv-button-skeleton
and a blank story

When I add skeleton to the export like:

export {
  CvButton,
  CvButtonConsts,
  CvButtonSet,
  CvIconButton,
  CvButtonSkeleton,
};

All works great!

Extra

For bonus points, since you are in that code anyway, ... could I ask for a separate fix unrelated to skeleton?
The main button stories are in src/components/CvButton/CvButton.stories.js but some of them have an issue. The button is blank like this:

The issue is that somehow we have

'slotArgs.default': 'Field size',

instead of

default: 'Field size',

Could you update the button stories to fix that too?

[OlkaB]

Thanks @davidnixon . Export added (sorry missed that).
The requested fix for buttons stories will be done in separate PR.

btw. As I'm not using github for PRs on a daily basis let me please know if I should do sth here (differently?)

[davidnixon]

I have not used that test.each pattern before. Very cool!