fix: Invalid handling of id in foreach when using discovery components

[thampiotr]

Brief description of Pull Request

In the foreach close there is an option to use id for each element off the collection. This requires looking at the element conceptually as a map and extracting the required id. But in Alloy unfortunately there are many ways of expressing an conceptual map. The key ways are:

• map[string]any: Inline object literals with simple values.

  • Example: collection = [{name = "one", port = "8080"}, {name = "two", port = "8081"}]

• map[string]string: Plain Go maps - used to be common, but are now replaced by Target capsules for performance. We keep it for maximum compatibility in case it's needed in the future.

• map[string]syntax.Value: Inline object literals with expressions or computed values.

  • Example: collection = [{name = "one", url = "http://" + hostname}]

• syntax.ConvertibleIntoCapsule: Capsules from component exports, such as discovery.Target.

  • Example: collection = discovery.kubernetes.pods.targets

Previously we didn't support or test them all. Now we do.

Fixes #5297

PR Checklist

• Documentation added
• Tests updated
• Config converters updated

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[Copilot]

Pull request overview

Fixes foreach ID extraction so id = "<field>" works consistently across different “map-like” collection item representations, including discovery target capsules.

Changes:

• Refactors ID extraction into collectionItemID with support for map[string]any, map[string]string, map[string]syntax.Value, and syntax.ConvertibleIntoCapsule.
• Updates existing foreach controller tests to use map[string]any and adds coverage for map[string]any and map[string]syntax.Value ID extraction.
• Adds a new external-package test validating ID extraction from discovery.Target capsules.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.

File	Description
internal/runtime/internal/controller/node_config_foreach.go	Adds generalized ID extraction helper to support capsules and additional map shapes.
internal/runtime/internal/controller/node_config_foreach_test.go	Updates scope map typing and adds tests for ID extraction from map[string]any and map[string]syntax.Value.
internal/runtime/internal/controller/foreach_targets_test.go	Adds external-package test to validate foreach ID extraction from discovery.Target capsules.