add new reusable workflow to test build of extensions in repos

[aalves08]

Summary

Fixes #15484

Occurred changes and/or fixed issues

• add new reusable workflow build-extensions-test.yml to test build of extensions in repos
• add workflow to creators package and bump creators version

Technical notes summary

• based on the work done in dashboard: https://github.com/rancher/dashboard/blob/reusab-workflow-test/.github/workflows/extensions-build-test.yaml

• tests with Elemental repository based on this PR: test workflow run elemental-ui#260

• usecase, no disable: https://github.com/rancher/elemental-ui/actions/runs/19233059508

• usecase, disabling only one of two extensions: https://github.com/rancher/elemental-ui/actions/runs/19232900365

• usecase, disabling all extensions: https://github.com/rancher/elemental-ui/actions/runs/19233033161

Areas or cases that should be tested

Areas which could experience regressions

Screenshot/Video

Checklist

• The PR is linked to an issue and the linked issue has a Milestone, or no issue is needed
• The PR has a Milestone
• The PR template has been filled out
• The PR has been self reviewed
• The PR has a reviewer assigned
• The PR has automated tests or clear instructions for manual tests and the linked issue has appropriate QA labels, or tests are not needed
• The PR has reviewed with UX and tested in light and dark mode, or there are no UX changes
• The PR has been reviewed in terms of Accessibility
• The PR has considered, and if applicable tested with, the three Global Roles Admin, Standard User and User Base

[mantis-toboggan-md]

LGTM - tested in the virtual clusters ui repo