BSB-Lan: Add timesync action integration documentation

[liudger]

Proposed change

This pull request adds documentation for a new action to the BSB-Lan integration, allowing users to synchronize the time on their BSB-Lan devices with Home Assistant's system time. This helps ensure accurate timestamps for device logs and schedules.

New action documentation:

• Added a section describing the bsblan.sync_time action, including its purpose, usage, and configuration options.
• Provided example YAML snippets for syncing time for all devices, a specific device, and scheduling the action in an automation.

Type of change

• Spelling, grammar or other readability improvements (current branch).
• Adjusted missing or incorrect information in the current documentation (current branch).
• Added documentation for a new integration I'm adding to Home Assistant (next branch).
  • I've opened up a PR to add logos and icons in Brands repository.
• Added documentation for a new feature I'm adding to Home Assistant (next branch).
• Removed stale or deprecated documentation.

Additional information

• Link to parent pull request in the codebase: Add time synchronization feature to BSB-Lan integration core#156600
• Link to parent pull request in the Brands repository:
• This PR fixes or closes issue: fixes #

Checklist

• This PR uses the correct branch, based on one of the following:
  • I made a change to the existing documentation and used the current branch.
  • I made a change that is related to an upcoming version of Home Assistant and used the next branch.
• The documentation follows the Home Assistant documentation standards.

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[Copilot]

Pull Request Overview

This pull request adds documentation for the new bsblan.sync_time action to the BSB-Lan integration. The action enables users to synchronize their BSB-Lan device's time with Home Assistant's system time, helping maintain accurate timestamps for heating system logs and schedules.

Key changes

• Added an "Actions" section to document the integration's available actions
• Documented the bsblan.sync_time action with clear descriptions, configuration options, and data attributes
• Provided three practical YAML examples: basic usage, device-specific sync, and automated daily synchronization