Allow to define global headers included in every request

lib/src/generators/client.dart

@@ -149,6 +149,7 @@ class $clientException implements io.HttpException {
     this.code,
     this.body,
   });
+  
   @override
   final String message;
   @override
@@ -188,23 +189,27 @@ class $clientException implements io.HttpException {
 class $clientName {
   $clientName({
     $authInputCode
-    String? baseUrl,
+    this.baseUrl,
+    this.globalHeaders = const {},
     http.Client? client,
   }) : assert(
           baseUrl == null || baseUrl.startsWith('http'),
           'baseUrl must start with http',
-        ) {
-    // Ensure trailing slash is removed from baseUrl
-    this.baseUrl = baseUrl?.replaceAll(RegExp(r'/\$'), '');
-    // Create a retry client
-    this.client = RetryClient(client ?? http.Client());
-  }
+        ),
+        assert(
+          baseUrl == null || !baseUrl.endsWith('/'),
+          'baseUrl must not end with /',
+        ),
+        client = RetryClient(client ?? http.Client());
 
   /// User provided override for baseUrl URL
-  late final String? baseUrl;
+  final String? baseUrl;
+  
+  /// Headers to be sent with every request
+  final Map<String, String> globalHeaders;
 
   /// HTTP client for requests
-  late final http.Client client;
+  final http.Client client;
   
   ${authVariables.isEmpty ? '' : '/// Authentication related variables'}
   ${authVariables.join('\n')}
@@ -290,6 +295,9 @@ class $clientName {
     if (responseType.isNotEmpty){
       headers['${HttpHeaders.acceptHeader}'] = responseType;
     }
+    
+    // Add global headers
+    headers.addAll(globalHeaders);
 
     // Build the request object
     late http.Response response;