chore: Switch review app to GitLab Pages multi deployments

Purpose

chore: Switch review app to GitLab Pages multi deployments

This switches from an nginx based workflow which requires a VM to a pages based workflow. Should also fix MRs from forks.

See also:

• gitlab-ui!4065 (merged)

chore: Fix base dir in review apps

Review apps will have a different pathname than /gitlab-svgs/. Porting the strategy from design.gitlab.com

ci: Move building of pages site to pages jobs

Otherwise the needed environment variable (CI_ENVIRONMENT_URL) is not available to nuxt.

Also this separates concerns: publish-to-npm job (and the dry-run) can run earlier.

1. build-and-check: Checks files and builds svgs for package
2. pages / review-app: Build pages site.

chore: Copy compiled assets to svgpreviewer directory

chore: remove duplicate unit

before it was rendering KiBkb.

Screenshots

N/A, see review apps link.

Checklist

For a new icon and/or illustration:

• Link to related design issue:
• If this adds an icon ensure that it follows the new icon checklists.
• If this adds an illustration ensure that it follows the new illustration checklists.

For third-party trademarks:

• If this adds or updates an icon or illustration that includes a third-party trademark, ensure that it follows the process for adding third-party trademarks to GitLab.