UI: Improve new Button component

[cdedreuille]

What I did

After a couple of tests, we would like to bring some updates on the Button component to make it easier to work with Storybook including these changes:

• Rename variants to solid, outline, ghost` to follow standard.
• Create a new <IconButton /> component to simplify types and use.
• Bring icons as props, removing the ability to add any icons and be able to control sizes if we want to.

How to test

1. Run this branch locally and run Storybook UI with yarn storybook:ui
2. Open Storybook in your browser
3. Access the Button component
4. Access the IconButton component

Checklist

• Make sure your changes are tested (stories and/or unit, integration, or end-to-end tests)
• Make sure to add/update documentation regarding your changes
• If you are deprecating/removing a feature, make sure to update
  MIGRATION.MD

Maintainers

• When this PR is ready for testing, make sure to add ci:normal, ci:merged or ci:daily GH label to it to run a specific set of sandboxes. The particular set of sandboxes can be found in code/lib/cli/src/sandbox-templates.ts
• Make sure this PR contains one of the labels below.

["cleanup", "BREAKING CHANGE", "feature request", "bug", "build", "documentation", "maintenance", "dependencies", "other"]

🦋 Canary release

This PR does not have a canary release associated. You can request a canary release of this pull request by mentioning the @storybookjs/core team here.

core team members can create a canary release here or locally with gh workflow run --repo storybookjs/storybook canary-release-pr.yml --field pr=<PR_NUMBER>

[kasperpeulen]

LGTM