[typescript] replace headers with same case-insensitive key to match http spec (#22393)

* replace headers with same caseinsensitive key to match http spec

* regenerate samples

* regenerate samples

* enable test for header case-insensitive replacement

* reduce redundant test comments

Author: davidgamero

modules/openapi-generator/src/main/resources/typescript/http/http.mustache

@@ -183,6 +183,13 @@ export class RequestContext {
     }
 
     public setHeaderParam(key: string, value: string): void  {
+        // Delete any existing headers with case-insensitive matching keys
+        const lowerKey = key.toLowerCase();
+        for (const existingKey in this.headers) {
+            if (existingKey.toLowerCase() === lowerKey) {
+                delete this.headers[existingKey];
+            }
+        }
         this.headers[key] = value;
     }