[DOC] - Write docs for idle-culling settings

[viniciusdc]

This issue aims to track docs around the idle culling feature in Nebari, its settings, and how to configure them in the nebari-config.yaml file. The implementation of this feature is based on the Make idle culler settings configurable from the nebari-config.yaml pull request #1689.

• Explain the idle culling feature in Nebari, including a link to the JupyterLab documentation on this topic.
• Explain how changing the settings affects the culling process.
• Describe how to configure these settings in the nebari-config.yaml file.
• Ensure that the documentation is clear and concise and that all information is accurate and up-to-date.