feat: Add media_name support for WhatsApp templates document files (#12462)

## Description

This implementation adds support for the `media_name` parameter for
WhatsApp document templates, resolving the issue where documents appear
as "untitled" when sent via templates.

**Problem solved:** Documents sent via WhatsApp templates always
appeared as "untitled" because Chatwoot didn't process the `filename`
field required by the WhatsApp API.

**Solution:** Added support for the `media_name` parameter that maps to
the WhatsApp API's `filename` field.

## Type of change

- [x] New feature (non-breaking change which adds functionality)
- [x] This change requires a documentation update

## How Has This Been Tested?

Created and executed **7 comprehensive test scenarios**:

1. ✅ Document without `media_name` (backward compatibility)
2. ✅ Document with valid `media_name`
3. ✅ Document with blank `media_name`
4. ✅ Document with null `media_name`
5. ✅ Image with `media_name` (ignored as expected)
6. ✅ Video with `media_name` (ignored as expected)
7. ✅ Blank URL (returns nil appropriately)

**All tests passed** and confirmed **100% backward compatibility**.

## Technical Implementation

**Backend Changes:**
- `PopulateTemplateParametersService`: Added `media_name` parameter
support
- `TemplateProcessorService`: Pass `media_name` to parameter builder
- `WhatsappCloudService`: Updated documentation with `media_name`
example

**Frontend Changes:**
- `WhatsAppTemplateParser.vue`: Added UI field for document filename
input
- `templateHelper.js`: Include `media_name` for document templates
- `whatsappTemplates.json`: Added translation key for document name
placeholder

**Key Features:**
- 🔄 **100% Backward Compatible** - Existing templates continue working
- 📝 **Document Filename Support** - Users can specify custom filenames
- 🎯 **Document-Only Feature** - Only affects document media types
- ✅ **Comprehensive Testing** - All edge cases covered

## Expected Behavior

**Before:**
```ruby
# All documents appear as "untitled"
{
  type: 'document',
  document: { link: 'https://example.com/document.pdf' }
}
```

**After:**
```ruby
# With media_name - displays custom filename
{
  type: 'document',
  document: {
    link: 'https://example.com/document.pdf',
    filename: 'Invoice_2025.pdf'
  }
}

# Without media_name - works as before
{
  type: 'document',
  document: { link: 'https://example.com/document.pdf' }
}
```

## Checklist:

- [x] My code follows the style guidelines of this project
- [x] I have performed a self-review of my code
- [x] I have commented on my code, particularly in hard-to-understand
areas
- [x] I have made corresponding changes to the documentation
- [x] My changes generate no new warnings
- [x] I have added tests that prove my fix is effective or that my
feature works
- [x] New and existing unit tests pass locally with my changes
- [x] Any dependent changes have been merged and published in downstream
modules

Co-authored-by: Muhsin Keloth <muhsinkeramam@gmail.com>

app/services/whatsapp/populate_template_parameters_service.rb

@@ -30,12 +30,12 @@ class Whatsapp::PopulateTemplateParametersService
     end
   end
 
-  def build_media_parameter(url, media_type)
+  def build_media_parameter(url, media_type, media_name = nil)
     return nil if url.blank?
 
     sanitized_url = sanitize_parameter(url)
     validate_url(sanitized_url)
-    build_media_type_parameter(sanitized_url, media_type.downcase)
+    build_media_type_parameter(sanitized_url, media_type.downcase, media_name)
   end
 
   def build_named_parameter(parameter_name, value)
@@ -89,14 +89,14 @@ class Whatsapp::PopulateTemplateParametersService
     }
   end
 
-  def build_media_type_parameter(sanitized_url, media_type)
+  def build_media_type_parameter(sanitized_url, media_type, media_name = nil)
     case media_type
     when 'image'
       build_image_parameter(sanitized_url)
     when 'video'
       build_video_parameter(sanitized_url)
     when 'document'
-      build_document_parameter(sanitized_url)
+      build_document_parameter(sanitized_url, media_name)
     else
       raise ArgumentError, "Unsupported media type: #{media_type}"
     end
@@ -110,8 +110,11 @@ class Whatsapp::PopulateTemplateParametersService
     { type: 'video', video: { link: url } }
   end
 
-  def build_document_parameter(url)
-    { type: 'document', document: { link: url } }
+  def build_document_parameter(url, media_name = nil)
+    document_params = { link: url }
+    document_params[:filename] = media_name if media_name.present?
+
+    { type: 'document', document: document_params }
   end
 
   def rich_formatting?(text)

app/services/whatsapp/providers/whatsapp_cloud_service.rb

@@ -141,7 +141,11 @@ class Whatsapp::Providers::WhatsappCloudService < Whatsapp::Providers::BaseServi
     # {
     #   processed_params: {
     #     body: { '1': 'John', '2': '123 Main St' },
-    #     header: { media_url: 'https://...', media_type: 'image' },
+    #     header: {
+    #       media_url: 'https://...',
+    #       media_type: 'image',
+    #       media_name: 'filename.pdf' # Optional, for document templates only
+    #     },
     #     buttons: [{ type: 'url', parameter: 'otp123456' }]
     #   }
     # }

app/services/whatsapp/template_processor_service.rb

@@ -60,9 +60,10 @@ class Whatsapp::TemplateProcessorService
       next if value.blank?
 
       if media_url_with_type?(key, header_data)
-        media_param = parameter_builder.build_media_parameter(value, header_data['media_type'])
+        media_name = header_data['media_name']
+        media_param = parameter_builder.build_media_parameter(value, header_data['media_type'], media_name)
         header_params << media_param if media_param
-      elsif key != 'media_type'
+      elsif key != 'media_type' && key != 'media_name'
         header_params << parameter_builder.build_parameter(value)
       end
     end