feat(bff): create endpoint to list all model versions

[ederign]

Description

This PR introduces a new endpoint to fetch all model versions:

# GET /api/v1/model_registry/{model_registry_id}/model_versions
curl -i -H "kubeflow-userid: [email protected]" "http://localhost:4000/api/v1/model_registry/model-registry/model_versions?namespace=kubeflow"

In this PR:

• clients/ui/bff/README.md: adding readme for new endpoint
• clients/ui/bff/internal/api/app.go: adding new route
• clients/ui/bff/internal/api/model_versions_handler.go: new handler to get all models version
• clients/ui/bff/internal/api/model_versions_handler_test.go: companion tests
• clients/ui/bff/internal/api/registered_models_handler.go: small rename to avoid clash
• clients/ui/bff/internal/mocks/model_registry_client_mock.go: mock implementation
• clients/ui/bff/internal/repositories/model_version.go : repository for get all model version (call to MR)
• clients/ui/bff/internal/repositories/model_version_test.go: companion tests
• clients/ui/bff/internal/repositories/registered_model.go: refactoring to avoid clash
• clients/ui/bff/internal/repositories/registered_model_test.go: refactoring to avoid clash

How Has This Been Tested?

With --mock-k8s-client=true --mock-mr-client=false:

http://localhost:4000/api/v1/model_registry/model-registry/model_versions?namespace=kubeflow
{
  "data": {
    "items": [
      {
        "author": "kubeflow-user",
        "createTimeSinceEpoch": "1729029766652",
        "customProperties": {
          
        },
        "description": "fsdfsd",
        "id": "4",
        "lastUpdateTimeSinceEpoch": "1729029766652",
        "name": "fsdfsd",
        "registeredModelId": "3",
        "state": "LIVE"
      },
    ...
    ],
    "nextPageToken": "",
    "pageSize": 0,
    "size": 8
  }
}
```

http://localhost:4000/api/v1/model_registry/model-registry/model_versions/4?namespace=kubeflow
{
"data": {
"author": "kubeflow-user",
"createTimeSinceEpoch": "1729029766652",
"customProperties": {

},
"description": "fsdfsd",
"id": "4",
"lastUpdateTimeSinceEpoch": "1729029766652",
"name": "fsdfsd",
"registeredModelId": "3",
"state": "LIVE"

}
}

## Merge criteria:
<!--- This PR will be merged by any repository approver when it meets all the points in the checklist -->
- All the commits have been [_signed-off_](https://github.com/kubeflow/community/tree/master/dco-signoff-hook#signing-off-commits)  (To pass the `DCO` check)

<!--- Go over all the following points, and put an `x` in all the boxes that apply. -->
- [ ] The commits have meaningful messages; the author will squash them after approval or in case of manual merges will ask to merge with squash.
- [ ] Testing instructions have been added in the PR body (for PRs involving changes that are not immediately obvious).
- [ ] The developer has manually tested the changes and verified that the changes work.
- [ ] Code changes follow the [kubeflow contribution guidelines](https://www.kubeflow.org/docs/about/contributing/).

If you have UI changes

<!--- You can ignore these if you are doing Go Model Registry REST server, MR Python client, manifest, controller, internal logic, etc changes; aka non-UI / visual changes -->
- [X] The developer has added tests or explained why testing cannot be added.
- [X] Included any necessary screenshots or gifs if it was a UI change.
- [X] Verify that UI/UX changes conform the UX guidelines for Kubeflow.

[lucferbux]

/lgtm

Tested and it's working, approving since i need it for my dev.

[google-oss-prow]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: lucferbux

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• clients/ui/OWNERS [lucferbux]

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