feat: add JSON output to taskrun delete

[Debashich]

Changes

Part of #2850

Add consistent -o/--output json support to taskrun delete, including machine-readable output of successfully deleted TaskRuns. Interactive confirmation prompts are suppressed when JSON output is requested.

Extend the shared deleter package with accessors for successful and related deletions, with corresponding unit tests.

Verified the relevant TaskRun delete/list output paths and existing test coverage. go test ./pkg/cmd/taskrun ./pkg/deleter passes.

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• Includes [tests](https://github.com/tektoncd/community/blob/master/standards.md#principles) (if functionality changed/added)
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• Commit messages follow [commit message best practices](https://github.com/tektoncd/community/blob/master/standards.md#commit-messages)

See [the contribution guide](https://github.com/tektoncd/cli/blob/master/CONTRIBUTING.md)
for more details.

Release Notes

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