Task

We should skip the `export` job for `/publish` when only metadata files are changed in a PR.

Background

When only making metadata changes (ex: changing support level of plugins), we need to run `/publish` to be able to merge PRs due to the github ruleset. For large workspaces like backstage, this can take quite a while so it would be nice to be able to skip the `export` and just validate the metadata instead. Ex: https://github.com/redhat-developer/rhdh-plugin-export-overlays/pull/2005

Dependencies and Blockers

QE impacted work
Documentation impacted work 

Acceptance Criteria

• Update overlays github workflows to skip export on `/publish` for metadata only PRs
• Still validate metadata using the existing `validate-metadata` action in export-utils