Add nested counter to order lists

[ilayda21]

Done

• Added nested counter to order lists

Fixes #4074

QA

• Open docs
• Open "Nested Count" section
• Verify item numbers are displayed correctly
• Open examples
• Verify item numbers are displayed correctly

Check if PR is ready for release

If this PR contains Vanilla SCSS code changes, it should contain the following changes to make sure it's ready for the release:

• PR should have one of the following labels to automatically categorise it in release notes:
  • Feature 🎁, Breaking Change 💣, Bug 🐛, Documentation 📝, Maintenance 🔨.
• Vanilla version in package.json should be updated relative to the most recent release, following semver convention:
  • if CSS class names are not changed it can be bugfix relesase (x.x.X)
  • if CSS class names are changed/added/removed it should be minor version (x.X.0)
  • see the wiki for more details
• Any changes to component class names (new patterns, variants, removed or added features) should be listed on the what's new page.
• Documentation side navigation should be updated with the relevant labels.

Screenshots

[webteam-app]

Demo starting at https://vanilla-framework-4264.demos.haus

[bartaz]

@ilayda21 @mtruj013 As this is a new "feature" we are adding new class name this is when the other items on PR checklist start to apply:

• We need to bump version to minor one, so 3.1.0 in this case
• We should add this to the top of the table in What's New page: https://vanillaframework.io/docs/whats-new
• We should add a "Updated" label to sidebar link to Lists page to mark that there is a new variant (here: https://github.com/canonical-web-and-design/vanilla-framework/blob/main/templates/_layouts/docs.html#L78)

[bartaz]

Can you link directly to the section?

Suggested change

	<th><a href="/docs/patterns/lists">Ordered list nested counter</a></th>
	<th><a href="/docs/patterns/lists#nested-count">Ordered list nested counter</a></th>

[ilayda21]

👍

[bartaz]

LGTM, just one tiny suggestion.
Thanks!