Update matrix-auth example

[anthony-chu]

Describe your use-case which is not covered by existing documentation.

Since version 3.2 of the matrix-auth plugin was released, the JCasC syntax for configuring permissions has been updated. The current documentation still refers to the pre-3.2 syntax. It should be noted, however, that you can use the deprecated: warn JCasC configuration to prevent errors from using a deprecated configuration, though it would be good to note that this older way of configuring is deprecated and the new configuration should be encouraged.

Reference any relevant documentation, other materials or issues/pull requests that can be used for inspiration.

Here is the example given in the matrix-auth 3.2 release notes:

authorizationStrategy:
  projectMatrix:
    entries:
      - user:
          name: "admin"
          permissions:
            - "Overall/Administer"
      - group:
          name: "authenticated"
          permissions:
            - "Overall/Read"

see https://github.com/jenkinsci/matrix-auth-plugin/releases/tag/matrix-auth-3.2