Add a new `size` prop with `sm` (current behaviour) as default.

feat: add `size` prop for `gl-breadcrumb`

See merge request gitlab-org/gitlab-ui!4954



Merged-by: Mark Florian <mflorian@gitlab.com>
Approved-by: Jacques Erasmus <jerasmus@gitlab.com>
Approved-by: Amelia Bauerly <abauerly@gitlab.com>
Approved-by: Savas Vedova <svedova@gitlab.com>
Approved-by: Mark Florian <mflorian@gitlab.com>
Reviewed-by: Mark Florian <mflorian@gitlab.com>
Co-authored-by: Chaoyue Zhao <czhao@gitlab.com>

# [108.1.0](gitlab-org/gitlab-ui@v108.0.1...v108.1.0) (2025-02-05)

### Features

* **GlBreadcrumb:** Add `size` prop ([47cf4bd6](gitlab-org/gitlab-ui@47cf4bd6))