bug: the namespace field in a Pipeline silently does nothing

[SaphMB]

When writing a Workflow Pipeline, if the user specifies a metadata.namespace, this field is silently ignored. At present, the documentation notes that the fields is optional, which is misleading.

When a namespace is specified, this should either:

• inform the user that the field will no be used and the documentation should align with this
  or
• create the resulting pipeline job in the specified namespace