Update documentation to match new playbook variable assignment

[YisDav]

Description

This PR updates the install-wazuh-cluster.rst file to modify the position of the filebeat_node_name variable in the Ansible role definitions. This ensures that the node name for Filebeat is correctly configured.

More information can be found in the related issue: wazuh/wazuh-ansible#1384

Checks

Docs building

• Compiles without warnings.

Code formatting and web optimization

• Uses three spaces indentation.
• Adds or updates meta descriptions accordingly.
• Updates the redirects.js script if necessary (check this guide).

Writing style

• Uses present tense, active voice, and semi-formal registry.
• Uses short, simple sentences.
• Uses bold for user interface elements, italics for key terms or emphasis, and code font for Bash commands, file names, REST paths, and code.

[javimed]

Please use bug/issueID-short-description for the branch name instead. Thanks