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

[greglittlefield-wf]

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

[aviary2-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

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

[trentgrover-wf]

+1
docs only change

@Workiva/release-management-pp

[trentgrover-wf]

failing dart 2 build due to analyzer fatal warnings...

[codecov-io]

Codecov Report

Merging #142 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #142   +/-   ##
=======================================
  Coverage   96.55%   96.55%           
=======================================
  Files           4        4           
  Lines         348      348           
=======================================
  Hits          336      336           
  Misses         12       12

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[greglittlefield-wf]

+1 @Workiva/release-management-pp

[maxwellpeterson-wf]

+1