fix: add OpenAPIModelName for PackageManifest to fix oc explain

[jianzhangbjz]

Description of the change:

The oc explain packagemanifests --api-version=packages.operators.coreos.com/v1 command was failing because:

1. The OpenAPI schema didn't have the x-kubernetes-group-version-kind extension
2. The NewDefinitionNamer couldn't find the matching model name in the OpenAPI definitions map

Motivation for the change:
To address openshift/operator-framework-olm#1208 (comment)

{  fail [github.com/openshift/origin/test/extended/cli/explain.go:608]: Unexpected error:
    <*errors.errorString | 0xc0015b8140>: 
    Error running oc --namespace=e2e-test-oc-explain-2xzmz --kubeconfig=/tmp/configfile168747619 explain packagemanifests --api-version=packages.operators.coreos.com/v1:
    StdOut>
    GROUP:      packages.operators.coreos.com
    KIND:       PackageManifest
    VERSION:    v1
    StdErr>
    error: GVK map[group:packages.operators.coreos.com kind:PackageManifest version:v1] not found in OpenAPI schema
    exit status 1
    : error: GVK map[group:packages.operators.coreos.com kind:PackageManifest version:v1] not found in OpenAPI schema
    {
        s: "Error running oc --namespace=e2e-test-oc-explain-2xzmz --kubeconfig=/tmp/configfile168747619 explain packagemanifests --api-version=packages.operators.coreos.com/v1:\nStdOut>\nGROUP:      packages.operators.coreos.com\nKIND:       PackageManifest\nVERSION:    v1\nStdErr>\nerror: GVK map[group:packages.operators.coreos.com kind:PackageManifest version:v1] not found in OpenAPI schema\nexit status 1\n: error: GVK map[group:packages.operators.coreos.com kind:PackageManifest version:v1] not found in OpenAPI schema",
    }

Architectural changes:

With this fix:

1. ToOpenAPIDefinitionName() calls OpenAPIModelName() which returns the canonical name
2. The generated OpenAPI uses the same name via v1.PackageManifest{}.OpenAPIModelName()
3. NewDefinitionNamer finds the match and adds the GVK extension
4. oc explain can now find the schema by GVK

Testing remarks:

Reviewer Checklist

• Implementation matches the proposed design, or proposal is updated to match implementation
• Sufficient unit test coverage
• Sufficient end-to-end test coverage
• Bug fixes are accompanied by regression test(s)
• e2e tests and flake fixes are accompanied evidence of flake testing, e.g. executing the test 100(0) times
• tech debt/todo is accompanied by issue link(s) in comments in the surrounding code
• Tests are comprehensible, e.g. Ginkgo DSL is being used appropriately
• Docs updated or added to /doc
• Commit messages sensible and descriptive
• Tests marked as [FLAKE] are truly flaky and have an issue
• Code is properly formatted

Assisted-By: Claude-Code

[openshift-ci]

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