[WIP]chore(backend): migrate GORM v1 to v2

[kaikaila]

Summary

This PR migrates the entire ORM layer of the Kubeflow Pipelines backend from GORM v1 (github.com/jinzhu/gorm) to GORM v2 (gorm.io/gorm), covering:

• ✅ All core model definitions in backend/src/apiserver/model
• ✅ Full migration of the Execution Cache system under backend/src/cache/...

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Migration Details

Models Migration (GORM v1 → v2)

• Replaced all gorm:"primary_key" with gorm:"primaryKey"
• Ensured sql.Null* fields are handled consistently (where applicable)
• Switched from deprecated NewRecord() to .Create().Error-based flow
• Updated all AutoMigrate() calls to conform to GORM v2 APIs
• Removed all legacy GORM v1 imports

Execution Cache Migration

• Updated NewFakeDB, ClientManager, and associated test helpers to GORM v2
• Migrated store logic in execution_cache_store.go to use db.Create(...).Scan(...) patterns
• Removed deprecated NewRecord() usage and added structured error wrapping
• Restored non-unique index on ExecutionCacheKey to match v1 behavior (tests rely on repeated keys + latest record retrieval)

Client Manager Migration

Changes • Remove manual index creation block in InitDBClient (client_manager.go). • Add type:varchar(191) + index:...,priority:... tags in: • model.Run.ExperimentId and model.Run.Namespace • model.RunDetails.Conditions and model.RunDetails.FinishedAtInSec • model.RunDetails.CreatedAtInSec • Add uniqueIndex:name_namespace_index,priority:... tags in model.Pipeline.Name and model.Pipeline.Namespace • Retain original index names for backward compatibility and least-surprise.

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Notes

This PR supersedes any previous model-level-only migration PRs (e.g., chore/orm-migrate-resource-reference) by consolidating all ORM transitions into a unified update.
It also ensures that GORM v1 is no longer referenced anywhere in the backend codebase.

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Checklist

• [x] All tests pass locally (go test ./backend/...)
• [x] go.mod and imports updated to use GORM v2
• [x] No GORM v1 usage remains
• [x] Migration is backward-compatible with existing data schema where possible

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[google-oss-prow[bot]]

Hi @kaikaila. Thanks for your PR.

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[google-oss-prow[bot]]

@kaikaila: Cannot trigger testing until a trusted user reviews the PR and leaves an /ok-to-test message.

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/retest

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[zazulam]

/ok-to-test

[kaikaila]

/retest

[kaikaila]

Hi @HumairAK I wanna bring this to your attention. In backend/src/apiserver/model/task.go line 26, the field name RunId ≠ column name RunUUID. This may cause confusion when using foreignKey: in GORM v2. Happy to refactor if we want to align them.

[kaikaila]

Closed in favor of #12013 with a more accurate branch name and scope. Please continue reviewing there!