feat: add support for x-tagGroups extension [TDX-8530]

[vaibhavrajsingh2001]

Summary

Add support for the OpenAPI x-tagGroups extension to group multiple endpoint tags under named sections in the sidebar.

Changes

• parse and preserve top-level x-tagGroups from OpenAPI specs
• update endpoint TOC generation to render nested groups: group → tag → operation
• when x-tagGroups is present:
  • only tags listed in a group are shown
  • untagged operations are hidden from endpoint navigation
  • unknown tags are skipped with a warning
• preserve existing behavior when x-tagGroups is not present
• keep existing multi-tag operation URL handling
• ensure nested sidebar groups expand correctly when the active path changes during scrolling
• add sandbox spec coverage using x-tagGroups
• add focused tests for grouped TOC generation and nested sidebar active-state behavior

Steps to verify

• open the sandbox with the multi-tags.yaml spec
• verify the sidebar shows endpoint tags grouped under the configured x-tagGroups sections
• scroll through endpoint content and verify the active sidebar item updates and expands correctly

Resolves: https://konghq.atlassian.net/browse/TDX-8530

Previews

[kongponents-bot]

Install the preview package from this PR

@kong/spec-renderer@pr-924