azure: Use default upload parameters to avoid consuming too much memory (#11251)

A lot of memory is consumed when uploading small files in parallel, use
the default upload parameters and add MINIO_AZURE_UPLOAD_CONCURRENCY for
users to tweak.

pkg/env/env.go

@@ -18,6 +18,7 @@
 package env
 
 import (
+	"strconv"
 	"strings"
 	"sync"
 )
@@ -75,6 +76,16 @@ func Get(key, defaultValue string) string {
 	return defaultValue
 }
 
+// GetInt returns an integer if found in the environment
+// and returns the default value otherwise.
+func GetInt(key string, defaultValue int) (int, error) {
+	v := Get(key, "")
+	if v == "" {
+		return defaultValue, nil
+	}
+	return strconv.Atoi(v)
+}
+
 // List all envs with a given prefix.
 func List(prefix string) (envs []string) {
 	for _, env := range Environ() {