otlploghttp: global OTLP endpoint with trailing slash produces double-slash path

[RedZapdos123]

Description:

On latest main, otlploghttp mishandles the global OTEL_EXPORTER_OTLP_ENDPOINT when the base URL ends with a trailing slash

If the endpoint is set to a base URL like http://host/prefix/, log export requests are sent to /prefix//v1/logs instead of /prefix/v1/logs

Steps to Reproduce:

1. Check out main at 524fc3c25
2. From PowerShell in the repository root, run:

   $repo = ((Get-Location).Path -replace '\\', '/')
   $root = Join-Path $env:TEMP 'otel-otlploghttp-trailing-slash-repro'
   Remove-Item -Recurse -Force $root -ErrorAction SilentlyContinue
   New-Item -ItemType Directory -Force -Path $root | Out-Null
   
   @"
   module example.com/otlploghttprepro
   
   go 1.25.0
   
   require (
       go.opentelemetry.io/otel v0.0.0
       go.opentelemetry.io/otel/sdk/log v0.0.0
       go.opentelemetry.io/otel/exporters/otlp/otlplog/otlploghttp v0.0.0
   )
   
   replace go.opentelemetry.io/otel => $repo
   replace go.opentelemetry.io/otel/sdk/log => $repo/sdk/log
   replace go.opentelemetry.io/otel/exporters/otlp/otlplog/otlploghttp => $repo/exporters/otlp/otlplog/otlploghttp
   "@ | Set-Content -Path (Join-Path $root 'go.mod')
   
   @"
   package main
   
   import (
       "context"
       "fmt"
       "net/http"
       "net/http/httptest"
       "os"
       "time"
   
       "go.opentelemetry.io/otel/attribute"
       "go.opentelemetry.io/otel/exporters/otlp/otlplog/otlploghttp"
       sdklog "go.opentelemetry.io/otel/sdk/log"
   )
   
   func main() {
       var gotPath string
       srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
           gotPath = r.URL.Path
           w.WriteHeader(http.StatusOK)
           _, _ = w.Write([]byte("{}"))
       }))
       defer srv.Close()
   
       if err := os.Setenv("OTEL_EXPORTER_OTLP_ENDPOINT", srv.URL+"/prefix/"); err != nil {
           panic(err)
       }
       defer os.Unsetenv("OTEL_EXPORTER_OTLP_ENDPOINT")
   
       exp, err := otlploghttp.New(context.Background(), otlploghttp.WithTimeout(time.Second))
       if err != nil {
           panic(err)
       }
   
       var rec sdklog.Record
       rec.SetBody(attribute.StringValue("x"))
   
       if err := exp.Export(context.Background(), []sdklog.Record{rec}); err != nil {
           panic(err)
       }
   
       fmt.Println(gotPath)
   }
   "@ | Set-Content -Path (Join-Path $root 'main.go')
   
   Push-Location $root
   go mod tidy
   go run .
   Pop-Location

Actual Behavior:

The repro prints:

/prefix//v1/logs

So the exporter sends logs to a path with a duplicated slash

Expected Behavior:

The exporter should normalize the global base endpoint path and send logs to:

/prefix/v1/logs

A trailing slash in the base OTEL_EXPORTER_OTLP_ENDPOINT should not produce a duplicated slash in the final OTLP logs path

Notes:

• exporters/otlp/otlplog/otlploghttp/config.go currently returns u.Path + "/v1/logs" in convPath
• If u.Path already ends with /, that produces /prefix//v1/logs
• The trace and metric OTLP HTTP exporters normalize the global endpoint base path instead of duplicating the slash
• This is separate from otlploghttp.WithEndpointURL does not default to "/v1/logs" #8537, which discussed WithEndpointURL(...) semantics for explicit in-code endpoint URLs
• This bug affects only the global OTEL_EXPORTER_OTLP_ENDPOINT base URL path handling

[RedZapdos123]

Opened a PR to resolve the issue.