feat(crons): Add owner field to MonitorConfig

[julwhitney13]

Summary

Adds support for the owner field in MonitorConfig to enable monitor ownership assignment to teams or users. This allows developers to organize and route cron monitors within their organization without needing to use the Sentry REST API separately.

Description

• Adds owner field (optional, format: "team:6" or "user:51") to MonitorConfig TypedDict
• Adds test verifying owner field is properly serialized in check-in payload
• Related PRs in sentry-docs:
  • Update Python crons documentation with owner field examples
  • Update Celery crons documentation with owner field example

Issues

• resolves: Support team assignment for cron monitors via SDK #5609
• resolves: PY-2126

Reminders

• Please add tests to validate your changes, and lint your code using tox -e linters.
• Add GH Issue ID & Linear ID (if applicable)
• PR title should use conventional commit style (feat:, fix:, ref:, meta:)
• For external contributors: CONTRIBUTING.md, Sentry SDK development docs, Discord community

[github-actions]

Semver Impact of This PR

🟡 Minor (new features)

📋 Changelog Preview

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New Features ✨

• (crons) Add owner field to MonitorConfig by julwhitney13 in #5610

Bug Fixes 🐛

• (celery) Propagate user-set headers by sentrivana in #5581
• (utils) Avoid double serialization of strings in safe_serialize by ericapisani in #5587

Documentation 📚

• (openai-agents) Remove inapplicable comment by alexander-alderman-webb in #5495
• Add AGENTS.md by sentrivana in #5579
• Add set_attribute example to changelog by sentrivana in #5578

Internal Changes 🔧

• (openai-agents) Expect namespace tool field for new openai versions by alexander-alderman-webb in #5599

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