[Backlog] Add ConfluencePS repository governance baseline

[lipkau]

Problem

ConfluencePS is missing core repository governance assets (maintainer guidance, contribution conventions, issue templates, and dependency hygiene automation), making maintenance and onboarding inconsistent.

Proposal

Add baseline repository governance files aligned with current AtlassianPS conventions.

Acceptance criteria

• Repository includes AGENTS.md, CONTRIBUTING.md, and CODEOWNERS.
• .github includes issue templates and a PR template.
• Dependabot configuration is present for GitHub Actions and PowerShell dependencies where applicable.
• README and contribution docs reference the current workflows and support model.