feat: add support to dynamic header on legacy config

experimental/packages/otlp-exporter-base/src/configuration/legacy-base-configuration.ts

@@ -14,7 +14,7 @@
  * limitations under the License.
  */
 export interface OTLPExporterConfigBase {
-  headers?: Record<string, string>;
+  headers?: Record<string, string> | (() => Record<string, string>);
   url?: string;
   concurrencyLimit?: number;
   /** Maximum time the OTLP exporter will wait for each batch export.

experimental/packages/otlp-exporter-base/src/configuration/shared-configuration.ts

@@ -42,12 +42,16 @@
 }
 
 export function wrapStaticHeadersInFunction(
-  headers: Record<string, string> | undefined
+  headers: Record<string, string> | (() => Record<string, string>) | undefined
 ): (() => Record<string, string>) | undefined {
   if (headers == null) {
     return undefined;
   }
 
+  if (headers instanceof Function) {
+    return headers;
+  }
+
   return () => headers;
 }