OTel: use semconv functions for filling out attributes

[morigs]

Currently, otel middleware add all the attributes manually.
I think it's better to use semconv functions for cases when fasthttp.Request is compatible with http.Request because this will automatically add all recommended attributes. This is easier to maintain because following spec requires semconv package update only.

Besides, I think it should use SpanStatusFromHTTPStatusCodeAndSpanKind instead of SpanStatusFromHTTPStatusCode

[WLun001]

@morigs fasthttp is not compatible with http
https://github.com/valyala/fasthttp#faq

[morigs]

This is very unfortunate 😞
At least, we should ensure that the set of attributes is the same

[efectn]

I think we can create same semconv methods that compatible with fasthttp.Request. But i'm not sure about that, i didn't review semconv's code much

[WLun001]

@morigs yes i have checked it. If you found out any missing attributes please feel free to create issues or PRs

[morigs]

@WLun001 awesome, thank you!