Add Breadcrumb docs

[auareyou]

Summary

Added a first version of the breadcrumb docs. A lot of the content is from the primer.style entry for Product UI breadcrumbs. This opens up an opportunity for an ADR on how to handle shared component documentation.

What should reviewers focus on?

For site designers

• Verify that the usage guidelines are aligned with the intended use for this component
• Verify that images represent examples the paint the full picture for this component

For Primer maintainers

• Files are located and named appropriately
• Links and images work properly
• Gut check on the content

Supporting resources (related issues, external links, etc):

• https://github.com/github/primer/issues/3219
• https://github.com/github/primer/issues/3214

Contributor checklist:

• [ ] All new and existing CI checks pass
• [ ] Tests prove that the feature works and covers both happy and unhappy paths
• [ ] Any drop in coverage, breaking changes or regressions have been documented above
• [ ] New visual snapshots have been generated / updated for any UI changes
• [ ] All developer debugging and non-functional logging has been removed
• [ ] Related issues have been referenced in the PR description

Reviewer checklist:

• [ ] Check that pull request and proposed changes adhere to our contribution guidelines and code of conduct
• [ ] Check that tests prove the feature works and covers both happy and unhappy paths
• [ ] Check that there aren't other open Pull Requests for the same update/change

Screenshots:

Please try to provide before and after screenshots or videos

Before	After

[changeset-bot[bot]]

⚠️ No Changeset found

Latest commit: c3d6d999ebe6984b5e2352f3716c5e20807f6df9

Merging this PR will not cause a version bump for any packages. If these changes should not result in a new version, you're good to go. If these changes should result in a version bump, you need to add a changeset.

This PR includes no changesets

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[github-actions[bot]]

🟢 No design token changes found

[github-actions[bot]]

🟢 No visual differences found

Our visual comparison tests did not find any differences in the UI.

[danielguillan]

Closing this PR in favor of #915