feat: Update issue and overview process documentation

[ADubhlaoich]

Proposed changes

This commit re-orders the issue templates, adds examples of issues and guidance on what templates should be used. It also adds a reference to the nginx.org content pipeline documentation that was stored in the folder but not linked from the newer index.

Checklist

Before sharing this pull request, I completed the following checklist:

• I read the Contributing guidelines
• My branch adheres to the Git conventions
• My content changes adhere to the F5 NGINX Documentation style guide
• If my changes involve potentially sensitive information¹, I have assessed the possible impact
• I have waited to ensure my changes pass tests, and addressed any discovered issues

Footnotes

1. Potentially sensitive information includes personally identify information (PII), authentication credentials, and live URLs. Refer to the style guide for guidance about placeholder content. ↩

[github-actions]

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