Update matrix-auth-plugin docs for v3.2+ syntax

[Junaid-Ashraf-56]

Description

Updates the matrix-auth-plugin documentation to reflect the new syntax introduced in matrix-auth plugin version 3.2.

What I Did

• Updated documentation to use the new entries: format for matrix-auth plugin 3.2+
• Added examples for both globalMatrix and projectMatrix configurations using the new syntax
• Included deprecated syntax examples for reference and migration guidance
• Fixed inconsistencies in the original examples
• Added a clear note about the syntax change at the top of the document

Changes Made

1. Global Matrix Example: Updated to use entries: with separate user/group configurations
2. Project Matrix Example: Updated to use entries: format and grouped permissions by principal
3. Deprecated Examples: Added clearly marked deprecated configuration examples for both matrix types
4. Migration Guidance: Added note about deprecated: warn option for backward compatibility

References

• matrix-auth 3.2 release notes: https://github.com/jenkinsci/matrix-auth-plugin/releases/tag/matrix-auth-3.2

Testing

The documentation updates follow the exact syntax provided in the official matrix-auth 3.2 release notes and maintain backward compatibility information for users migrating from older versions.

[Junaid-Ashraf-56]

Please review my pull request, and if any problem, please guide me.

[timja]

Thanks for this PR! It looks good, few minor changes that would make this better.

[timja]

Could you update the integration test to use this to prove it works please (and continues to work):

https://github.com/jenkinsci/configuration-as-code-plugin/blob/master/integrations/src/test/java/io/jenkins/plugins/casc/ProjectMatrixAuthorizationTest.java

It will need to change to use the JenkinsConfiguredWithReadmeRule

You can then append #<heading-number> to the ConfiguredWithReadme so that it uses the right example, like in:

configuration-as-code-plugin/integrations/src/test/java/io/jenkins/plugins/casc/GitHostKeyVerificationTest.java

Line 22 in 4cb0061

@ConfiguredWithReadme("git-client/README.md#2")

[Junaid-Ashraf-56]

It is a pleasure for me to work on the repo.

[timja]

you haven't done this

[Junaid-Ashraf-56]

Thank you @timja for your thoughtful review and guidance throughout this PR.

[timja]

Please don't mark comments as resolved until you've pushed the fix

[Junaid-Ashraf-56]

I have updated the pr according to the requirement.