🚀 [Feature]: Custom metric attributes for otelfiber

[hwo411]

Feature Description

We want to be able to add additional attributes to the metrics exported by otelfiber similar to WithCustomAttrributes for span.

Additional Context (optional)

In our case we want to set a custom parameter based on request body parameter, and it's currently impossible. We either have to reimplement the metrics ourselves via custom middleware or fork the library and use the updated fork.

Code Snippet (optional)

otelfiber.Middleware(otelfiber.WithCustomRequestMetricAttributes(...), otelfiber.WithCustomResponseMetricAttributes(...))
// or
otelfiber.Middleware(otelfiber.WithCustomMetricAttributes(...))

Checklist:

• I agree to follow Fiber's Code of Conduct.
• I have checked for existing issues that describe my suggestion prior to opening this one.
• I understand that improperly formatted feature requests may be closed without explanation.