Metrics updates

[dmytro-landiak]

Pull Request description

This PR introduces major improvements to how TBMQ tracks, structures, and presents metrics, with a focus on more accurate payload-level observability and a cleaner UI/UX in the Monitoring and Home dashboards.

Key Changes

1. Enhanced metric tracking and counting

• Reworked the internal logic for collecting metrics to improve accuracy and consistency.
• Introduced clearer separation of responsibilities in the metric pipeline.

2. New payload-oriented traffic metrics

• Removed the old network traffic metric.
• Added two new metrics: incoming payload traffic and outgoing payload traffic.
  These better reflect real data flow by counting only actual payload bytes, excluding control packets.
  This provides more meaningful insights into client load and bandwidth consumption.

3. Monitoring UI improvements

• The Monitoring page now contains two separate tabs, grouping graphs logically according to their domain.
• Labels, tooltips, and hints across graphs were updated for clarity and consistency.
• Added a *new graph for retained messages.

4. Home page graph refactoring

• Refactored and optimized all charts on the Home page.
• Reordered graphs based on priority to highlight the most important operational metrics.

General checklist

• You have reviewed the guidelines document.
• Labels that classify your pull request have been added.
• The milestone is specified and corresponds to fix version.
• Description references specific issue.
• Description contains human-readable scope of changes.
• Description contains brief notes about what needs to be added to the documentation.
• No merge conflicts, commented blocks of code, code formatting issues.
• Changes are backward compatible or upgrade script is provided.

Front-End feature checklist

• Screenshots with affected component(s) are added. The best option is to provide 2 screens: before and after changes;
• If you change the widget or other API, ensure it is backward-compatible or upgrade script is present.

Back-End feature checklist

• Added corresponding unit and/or integration test(s). Provide written explanation in the PR description if you have failed to add tests.
• If new dependency was added: the dependency tree is checked for conflicts.