Why:

This change updates the JFrog OIDC integration guide to reflect a recent improvement in the jfrog/setup-jfrog-cli GitHub Action. The action now supports seamless OIDC authentication out of the box, removing the need for users to manually exchange tokens via REST API calls.

What's being changed (if available, include any code snippets, screenshots, or gifs):

• Removed outdated examples that manually exchange the GitHub OIDC token using curl.
• Added a simplified and secure example using jfrog/setup-jfrog-cli@v4 with oidc-provider-name and oidc-audience inputs.
• Clarified that no manual token exchange is required when using the JFrog CLI.
• Added a permissions block (id-token: write) to the YAML example to ensure OIDC works as expected.
• Included a new “Security Best Practices” section and a “Further Reading” section linking to the JFrog CLI’s manual token exchange command for advanced use cases.

Check off the following:

• A subject matter expert (SME) has reviewed the technical accuracy of the content in this PR.
• The changes in this PR meet [the docs fundamentals that are required for all content](http://docs.github.com./en/contributing/writing-for-github-docs/about-githubs-documentation-fundamentals).
• All CI checks are passing and the changes look good in the review environment.