feat(kstepper): introduce kui tokens [KHCP-7725]

[portikM]

Summary

Addresses: https://konghq.atlassian.net/browse/KHCP-7725

Changes:

• introduces kui- design tokens in KStepper component
• removes any usage of Kongponents utility classes in KStepper component template

PR Checklist

• Conventional Commits all commits follow the conventional commit standards outlined in the main README.
• Functional: all changes do not break existing APIs and if so, bump major version.
• Tests pass: check the output of yarn test
• Naming: the files and the method and prop variables use the same naming conventions as other Kongponents
• Framework style: abides by the essential rules in Vue's style guide
• Cleanliness: does not have formatting issues, unused code (e.g., console.logs, debugger), or leftover comments
• Docs: includes a technically accurate README, uses JSDOC where appropriate

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[kongponents-bot]

🎉 This PR is included in version 8.119.0 🎉

The release is available on:

• npm package (@latest dist-tag)
• GitHub release

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