Pass explicit platforms list when publishing images
Pass explicit platforms list when publishing images

Prior to this commit the pipeline-release Pipeline relied on default
params to ensure that the publish-release task emits a windows
entrypoint image. It looks like this no longer works because the
dogfooding cluster is using alpha API fields, including implicit params.

With implicit params it is not possible to _skip_ a param in a PipelineTask if it
shares a name with a Param in the Pipeline. So before we were intentionally omitting the
platforms param and relying on the default param value in the
publish-release Task but with implicit params this is no longer
possible.

This commit overrides the param passed to publish-release with the full
string of platforms including windows. We don't want to update the
Pipeline's `platforms` param because our build-images
PipelineTask can't build the windows image. Confusing.

tektoncd/pipeline,tektoncd/pipeline