Added offline installation with the assistant

[davidcr01]

Description

Related issue: wazuh/wazuh-packages#1422
The aim of this PR is to add the documentation related to the Offline installation using the Wazuh installation assistant.

Before, the offline installation was documented step by step. Now, with the new --offline-install option of the Wazuh installation assistant, the Offline installation can be performed with this tool, so the related documentation is added.

Now, the Offline installation has an index page with the common steps, and in is split into two pages:

• Step-by-step installation.
• Using the assistant.

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.