[Bug]: `config.Configuration.InitGlobalTracer` panics if `http.DefaultTransport` is not a `*http.Transport`

[colega]

What happened?

I called config.Configuration.InitGlobalTracer(...) after replacing the http.DefaultTransport with a custom implementation, and it panicked.

The code assumes that http.DefaultTransport is a *http.Transport, and panics otherwise:

https://github.com/jaegertracing/jaeger-client-go/blob/8d8e8fcfd04de42b8482476abac6a902fca47c18/sampler_remote.go#L308

Steps to reproduce

1. Replace http.DefaultTransport value in your app.
2. Call config.Configuration.InitGlobalTracer()

Example: https://go.dev/play/p/TH-uFyyMuLD

package main

import (
    "fmt"
    "net/http"

    "github.com/uber/jaeger-client-go/config"
)

func main() {
    http.DefaultTransport = &customTransport{&http.Transport{}}
    closer, err := config.Configuration{}.InitGlobalTracer("hello-world")
    if err != nil {
        panic(fmt.Errorf("failed: %w", err))
    }
    defer closer.Close()

    fmt.Println("Hello, 世界")
}

type customTransport struct {
    next http.RoundTripper
}

func (ct *customTransport) RoundTrip(req *http.Request) (*http.Response, error) {
    return ct.next.RoundTrip(req)
}

Expected behavior

It shouldn't panic.

Relevant log output

No response

Screenshot

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Additional context

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Jaeger backend version

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SDK

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Pipeline

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Stogage backend

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Operating system

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Deployment model

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Deployment configs

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