Add support for a default storeSecret location in global ClusterImagePolicy

[riyaz967]

Currently portieris cluster policy don't have capability to reference storesecret from default or reference it from any other ns.
we are beating the use case of clusterpolicy if it is not there to reference it from default.
we need to have same capability what we have for keySecretNamespace where it can be referenced from portieris name space or default.