Support Pipeline Dependencies from different namespaces

[aidandunlop]

Is your feature request related to a problem? Please describe.
We'd like to use Pipeline Dependencies to import artefacts from Pipelines in a different namespace to the Pipeline they are being imported from. Currently this is limited to both source and destination Pipelines existing in the same namespace.

Describe the solution you'd like
The ability to configure the namespace of the source pipeline in runConfigurationRef and triggers.runConfigurations

Describe alternatives you've considered
None - current workaround is to deploy all pipelines from the same namespace

Additional context
This feature is useful for model ensembling where we can import a foundational model and fine-tuning it for different purposes. It's helpful to organise these Pipelines into separate namespaces.

[grahamia]

This could be done as part of the provider work.