Fix release task by copying input bucket contents
Fix release task by copying input bucket contents

Pipeline 0.7 does not automatically copy input contents to
the output folder for resources that are used both as input as
well as output. See tektoncd/pipeline#1118.

This change updates the release publish task to manually copy over
the contents of the input release bucket.

Signed-off-by: Dibyo Mukherjee <7d445be0c0af41c00c371a1f7b3669c3331901f5@google.com>

tektoncd/triggers,tektoncd/triggers