add docs for smoke testing of sso authentication

[nabim777]

Description

This PR adds documentation for smoke testing the Single-Sign-On through OpenID Connect Identity Provider.

Related Issue or Workpackage

• https://community.openproject.org/projects/nextcloud-integration/work_packages/64469

Screenshots (if appropriate):

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Tests only (no source changes)

Checklist:

• Code changes
• Unit tests added
• Acceptance tests added
• Updated CHANGELOG.md file

[github-actions]

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