[feature]: Spike Shipment Methods schould be expandable

[larsroettig]

Is your feature request related to a problem? Please describe.
As partner developer I want to have a simple possibility to extend shipments for venia-ui

Describe the solution you'd like
Research possibility and Problems of extending shipments how a public interface should look like.

Describe alternatives you've considered

Additional context
Add any other context or screenshots about the feature request here.

Please let us know what packages this feature is in regards to:

• venia-concept
• venia-ui
• pwa-buildpack
• peregrine
• pwa-devdocs
• upward-js
• upward-spec
• create-pwa

[m2-assistant]

Hi @larsroettig. Thank you for your report.
To help us process this issue please make sure that you provided sufficient information.

Please, add a comment to assign the issue: @magento I am working on this

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