provide PR link in git-open-pr promotion step output

[Marvin9]

Checklist

• I've searched the issue queue to verify this is not a duplicate bug report.
• I've included steps to reproduce the bug.
• I've pasted the output of kargo version.
• I've pasted logs, if applicable.

Description

Pull request deep links are not working - #3024 (comment)

With promotion steps, UI recently changed the way it structures Pull request deep link - #3024.

It constructs URL from git-open-pr step output and config values (repoURL from step config and prNumber from output). However when the spec contains expression language, it fails to generate URL because now repoURL is not raw value.

The solution is to provide as much as info in promotion steps output (in this case, repoURL), it can be either full URL or at the very least, values that will help UI to construct link.

Screenshots

#3024 (comment)

Steps to Reproduce

• Create stage with promotion step git-open-pr and promote to that stage
• check the promotion lists in stage details page and open the promotion step modal. Both won't have PR deep link

Version

dev