CPLAT-3300: CP Code Review and PR Merging Team agreement update

[kealjones-wk]

Client Platform is refreshing our contributing instructions as a result of solidifying our internal CP Code Review
and PR Merging Team agreement.

You can view the Details in this RFD: https://docs.google.com/document/d/1zQ9gMMnQo3AyYQfCThCwB76aYpU3BMmqm1faD5EA8bU/edit

This PR aligns the CONTRIBUTING.md and PULL_REQUEST_TEMPLATE.md with the new agreement.

• Removes all existing potential variations of CONTRIBUTING, PULL_REQUEST_TEMPLATE, and CODEOWNERS.

• Adds standardized PULL_REQUEST_TEMPLATE.md and CONTRIBUTING.md

[aviary-wf]

Security Insights

No security relevant content was detected by automated scans.

Action Items

• Review PR for security impact; comment "security review required" if needed or unsure
• Verify aviary.yaml coverage of security relevant code

---

Questions or Comments? Reach out on Slack: #support-infosec.

[trentgrover-wf]

+1
docs only change

@Workiva/release-management-pp