fix: Better linking of resources

[jedevc]

We don't need all this super weird stuff where we have to manually iterate to create the fields. We can just do this automatically in FieldsFromStruct.

[Copilot]

Pull request overview

This PR refactors resource linking so that links can be detected automatically during FieldsFromStruct processing, removing a lot of per-resource manual link wiring.

Changes:

• Replace resource.Link (struct) with a resource.Link interface and update consumers (TUI, sandbox cleanup, JSON marshaling).
• Enhance FieldsFromStruct to (a) flatten anonymous embedded structs and (b) detect Link implementations and bubble links appropriately.
• Introduce generic link helper types in internal/cmd/link.go and migrate several resources (instances, services, volumes, templates, certificates) to use them; update/extend tests and golden outputs.

Reviewed changes

Copilot reviewed 19 out of 22 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
internal/types/image.go	Adds Link() to ImageRef so image fields can auto-produce links.
internal/resource/value/format.go	Avoids panics by handling nil / nil-pointer values before interface checks.
internal/resource/tui/panel_detail.go	Switches TUI link tracking to resource.Link interface and resolves link targets via Link().
internal/resource/struct_test.go	Adds coverage for anonymous embedded structs and link detection/bubbling behavior.
internal/resource/struct.go	Refactors struct-to-fields conversion, adds centralized link detection, and flattens anonymous embeddings.
internal/resource/sandbox.go	Updates sandbox link traversal to use Link() and derived key strings.
internal/resource/resource.go	Replaces Link struct with Link interface and adds Field.MarshalJSON() to serialize links.
internal/cmd/volumes.go	Migrates volume fields/refs to LinkName and embedded Link[Instance], removing manual link construction.
internal/cmd/volume_templates.go	Migrates metro reference to LinkName and removes manual metro linking.
internal/cmd/services.go	Migrates metro and nested refs (instances/certificates) to embedded Link[...], removing manual link construction.
internal/cmd/link.go	Introduces generic Link[T] and LinkName[T] types implementing resource.Link.
internal/cmd/instances.go	Migrates metro to LinkName and replaces manual link construction with auto-linking; retains hyperlink behavior.
internal/cmd/instance_templates.go	Migrates metro to LinkName and removes manual link construction.
internal/cmd/certificates.go	Migrates metro to LinkName and removes manual link construction.
cmd/unikraft/testdata/TestGolden/volumes/import/serve	Golden output update reflecting field ordering changes.
cmd/unikraft/testdata/TestGolden/instances/volume-inline	Adds golden case for inline volume create/inspect/delete.
cmd/unikraft/testdata/TestGolden/instances/volume	Adds golden case for named volume attach flow.
cmd/unikraft/testdata/TestGolden/instances/help	Golden output update reflecting field ordering changes.
cmd/unikraft/testdata/TestGolden/instances/connect	Golden output update reflecting field ordering changes.
cmd/unikraft/testdata/TestGolden/instances/autostart	Adds golden case for autostart create/inspect/delete.
cmd/unikraft/testdata/TestGolden/instances/add-domain	Golden output update reflecting field ordering changes.
cmd/unikraft/instances_test.go	Renames subtests for new/updated instance golden scenarios.

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[craciunoiuc]

Good to go after the typo is fixed.

Reviewed-by: Cezar Craciunoiu cezar.craciunoiu@unikraft.com
Approved-by: Cezar Craciunoiu cezar.craciunoiu@unikraft.com