Make sure images stored in registry mirrors are signed
Make sure images stored in registry mirrors are signed

We were't previously signing these images because we weren't storing them in the `IMAGES` result when releaseAsLatest=true.

Since releaseAsLatest=true by default for releases, these images were never getting signed.

This change includes mirror images in the result, so they should be picked up by Chains and signed from now on.

tektoncd/pipeline,tektoncd/pipeline