Add consistent --output json support to all tkn commands

Summary

Not all tkn commands support --output json. This makes it unreliable for AI agents and scripts that need machine-readable output.

Current State

• start --dry-run supports --output json/yaml
• list commands use Go template tables, some support --output via PrintObjects
• describe commands have custom formatted output, some support --output via PrintObjectV1
• logs, delete, cancel have no structured output

Proposal

1. Add --output json and --output yaml to every command that produces output
2. Auto-detect non-TTY stdout and default to JSON (opt-out with --output table)
3. Support TKN_OUTPUT_FORMAT=json environment variable for session-wide default
4. Ensure all JSON output goes to stdout, all status/progress messages to stderr

Commands to update

• pipeline list/describe/start/delete
• pipelinerun list/describe/delete/cancel/logs
• task list/describe/start/delete
• taskrun list/describe/delete/cancel/logs
• customrun list/describe/delete
• bundle list/push
• eventlistener list/describe
• triggerbinding list/describe
• triggertemplate list/describe
• clustertriggerbinding list/describe

/kind feature

Start by inventorying the listed pipeline, pipelinerun, task, taskrun, customrun, bundle, eventlistener, triggerbinding, triggertemplate, and clustertriggerbinding commands, comparing existing PrintObjects and PrintObjectV1 support with commands such as logs, delete, and cancel. Done means every listed output-producing command supports JSON and YAML, non-TTY output defaults to JSON with a table opt-out, TKN_OUTPUT_FORMAT is honored, and JSON uses stdout while status messages use stderr.