add example for notifications

[Constey]

add an example to disable notifications for a rule but only one specific server.

Description

Checks

Docs building

• [x] Compiles without warnings.

Code formatting and web optimization

• [x] Uses three spaces indentation.
• [x] Adds or updates meta descriptions accordingly.
• [x] 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.
• [x] 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]

@Constey we need an associated issue raising the problem. Please create an issue associating with this PR if necessary. Take into consideration that not every use case needs to be explicitly included in the documentation. In this case, it seems enough to consult the hostname definition and syntax in https://documentation.wazuh.com/current/user-manual/ruleset/ruleset-xml-syntax/rules.html#rules-hostname to understand its uses.

Thank you.