static metrics attributes not supported

[stevenh]

Environment info:

• KrakenD version: 2.7.0 container
• System info: docker 27.1.1
• Hardware specs: Number of CPUs, RAM, etc
• Backend technology: Go
• Additional environment information:

Describe the bug
The documentation details that its possible to use static global metrics here however the GlobalConfig.MetricsStaticAttributes field that's need for plugins to use these is missing in the latest release of krakend-ce v2.7.0.

This field is present in the latest version of krakend-otel v0.6.0 but krakend-ce is still using v0.5.0 so I suspect that this functionality, even though documented, doesn't actually work, and certainly can't be accessed by plugins using:

state.GlobalConfig().GlobalOpts().MetricsStaticAttributes