[metrics] add namespace, subsystem and refactor names

[axelfahy]

trafficstars

Proposed changes

• Add namespace and subsystem for prometheus metrics
• Rename metrics according to prometheus guidelines

Related issues

• N/A

Checklist

• [x] I consider the submitted work as finished
• [x] I tested the code for its functionality
• [ ] I wrote test cases for the relevant uses case
• [ ] I added/update the relevant documentation (either on github or on notion)
• [ ] Where necessary I refactored code to improve the overall quality